# Quantum Physics

## New submissions

[ total of 73 entries: 1-73 ]
[ showing up to 2000 entries per page: fewer | more ]

### New submissions for Tue, 20 Mar 18

[1]
Title: A local $ψ$-epistemic retrocasual hidden-variable model of Bell correlations with wavefunctions in physical space
Authors: Indrajit Sen
Subjects: Quantum Physics (quant-ph)

We construct a local $\psi$-epistemic hidden-variable model of Bell correlations by a retrocausal adaptation of the originally superdeterministic model given by Brans. In our model, for a pair of particles the joint quantum state $|\psi_e(t)\rangle$ as determined by preparation is epistemic. The model also assigns to the pair of particles a factorisable joint quantum state $|\psi_o(t)\rangle$ which is different from the prepared quantum state $|\psi_e(t)\rangle$ and has an ontic status. The ontic state of a single particle consists of two parts. First, a single particle ontic quantum state $\chi(\vec{x},t)|i\rangle$, where $\chi(\vec{x},t)$ is a 3-space wavepacket and $|i\rangle$ is a spin eigenstate of the future measurement setting. Second, a particle position in 3-space $\vec{x}(t)$, which evolves via a de Broglie-Bohm type guidance equation with the 3-space wavepacket $\chi(\vec{x},t)$ acting as a local pilot wave. The joint ontic quantum state $|\psi_o(t)\rangle$ fixes the measurement outcomes deterministically whereas the prepared quantum state $|\psi_e(t)\rangle$ determines the distribution of the $|\psi_o(t)\rangle$'s over an ensemble. Both $|\psi_o(t)\rangle$ and $|\psi_e(t)\rangle$ evolve via the Schrodinger equation. Our model exactly reproduces the Bell correlations for any pair of measurement settings. We also consider non-equilibrium' extensions of the model with an arbitrary distribution of hidden variables. We show that, in non-equilibrium, the model generally violates no-signalling constraints while remaining local with respect to both ontology and interaction between particles. We argue that our model shares some structural similarities with the modal class of interpretations of quantum mechanics.

[2]
Title: PT-symmetric phase transition, hysteresis and bound states in the continuum
Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph)

We explicate the merging of levels and spectral bifurcation near an exceptional point as also the appearance of resonances and bound states in the PT-broken phase for the PT-symmetric complex Scarf II potential. The bound states in the PT-broken phase are manifested as spectral singularities and are found to be bound states in continuum and thus seen as zero width resonances, starting to first appear at the exceptional points. The intimate connection of PT-symmetry breaking and breaking of supersymmetry is pointed out as also the phenomenon of hysteresis near exceptional point. Intriguingly, the PT-symmetric Hamiltonians related by SUSY are also found to be isospectrally deformed counterparts for a specific parametric condition with the deformation satisfying the Korteweg-deVries equation.

[3]
Title: Two-color electromagnetically induced transparency via modulated coupling between a mechanical resonator and a qubit
Subjects: Quantum Physics (quant-ph)

We discuss level splitting and sideband transitions induced by a modulated coupling between a superconducting quantum circuit and a nanomechanical resonator. First, we show how to achieve an unconventional time-dependent longitudinal coupling between a flux (transmon) qubit and the resonator. Considering a sinusoidal modulation of the coupling strength, we find that a first-order sideband transition can be split into two. Moreover, under the driving of a red-detuned field, we discuss the optical response of the qubit for a resonant probe field. We show that level splitting induced by modulating this longitudinal coupling can enable two-color electromagnetically induced transparency (EIT), in addition to single-color EIT. In contrast to standard predictions of two-color EIT in atomic systems, we apply here only a single drive (control) field. The monochromatic modulation of the coupling strength is equivalent to employing two eigenfrequency-tunable mechanical resonators. Both drive-probe detuning for single-color EIT and the distance between transparent windows for two-color EIT, can be adjusted by tuning the modulation frequency of the coupling.

[4]
Title: From nonholonomic quantum constraint to canonical variables of photons I: true intrinsic degree of freedom
Subjects: Quantum Physics (quant-ph); Representation Theory (math.RT); Optics (physics.optics)

We report that the true intrinsic degree of freedom of the photon is neither the polarization nor the spin. It describes a local property in momentum space and is represented in the local representation by the Pauli matrices. This result is achieved by treating the transversality condition on the vector wavefunction as a nonholonomic quantum constraint. We find that the quantum constraint makes it possible to generalize the Stokes parameters to characterize the polarization of a general state. Unexpectedly, the generalized Stokes parameters are specified in a momentum-space local reference system that is fixed by another degree of freedom, called Stratton vector. Only constant Stokes parameters in one particular local reference system can convey the intrinsic degree of freedom of the photon. We show that the optical rotation is one of such processes that change the Stratton vector with the intrinsic quantum number remaining fixed. Changing the Stratton vector of the eigenstate of the helicity will give rise to a Berry's phase.

[5]
Title: Designing Quantum Router in IBM Quantum Computer
Subjects: Quantum Physics (quant-ph)

Quantum router is an essential ingredient in a quantum network. Here, we propose a new quantum circuit for designing quantum router by using IBM's five-qubit quantum computer. We design an equivalent quantum circuit, by the means of single-qubit and two-qubit quantum gates, which can perform the operation of a quantum router. Here, we show the routing of signal information in two different paths (two signal qubits) which is directed by a control qubit. According to the process of routing, the signal information is found to be in a coherent superposition of two paths. We demonstrate the quantum nature of the router by illustrating the entanglement between the control qubit and the two signal qubits (two paths), and confirm the well preservation of the signal information in either of the two paths after the routing process. We perform quantum state tomography to verify the generation of entanglement and preservation of information. It is found that the experimental results are obtained with good fidelity.

[6]
Title: Perpetual emulation threshold of PT-symmetric Hamiltonians
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)

We describe a technique to emulate a two-level \PT-symmetric spin Hamiltonian, replete with gain and loss, using only the unitary dynamics of a larger quantum system. This we achieve by embedding the two-level system in question in a subspace of a four-level Hamiltonian. Using an \textit{amplitude recycling} scheme that couples the levels exterior to the \PT-symmetric subspace, we show that it is possible to emulate the desired behaviour of the \PT-symmetric Hamiltonian without depleting the exterior, reservoir levels. We are thus able to extend the emulation time indefinitely, despite the non-unitary \PT dynamics. We propose a realistic experimental implementation using dynamically decoupled magnetic sublevels of ultracold atoms.

[7]
Title: Single-Photon-Triggered Quantum Phase Transition
Comments: 7 pages, 5 figures, the initial submitted time (to journal) April 24, 2017
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)

We propose a hybrid quantum model combining cavity QED and optomechanics, which allows the occurrence of equilibrium superradiant quantum phase transition (QPT) triggered by a single photon. This single-photon-triggered QPT exists both in the cases of ignoring and including the so-called $A^2$ term, i.e., it is immune to the no-go theorem. It originally comes from the photon-dependent quantum criticality featured by the proposed hybrid quantum model. Moreover, a reversed superradiant QPT is induced by the competition between the introduced $A^2$ term and the optomechanical interaction. This work offers an approach to manipulate QPT with a single photon, which should inspire the exploration of single-photon quantum-criticality physics and the engineering of new single-photon quantum devices.

[8]
Title: Blind quantum computing can always be made verifiable
Authors: Tomoyuki Morimae
Subjects: Quantum Physics (quant-ph)

Blind quantum computing enables a client, who does not have enough quantum technologies, to delegate her quantum computing to a remote quantum server in such a way that her privacy is protected against the server. Some blind quantum computing protocols can be made verifiable, which means that the client can check the correctness of server's quantum computing. Can any blind protocol always be made verifiable? In this paper, we answer to the open problem affirmatively. We propose a plug-in that makes any universal blind quantum computing protocol automatically verifiable. The idea is that the client blindly generates Feynman-Kitaev history states corresponding to the quantum circuit that solves client's problem and its complement circuit. The client can learn the solution of the problem and verify its correctness at the same time by measuring energies of local Hamiltonians on these states. Measuring energies of local Hamiltonians can be done with only single qubit measurements of Pauli operators.

[9]
Title: Photon blockade effect in a coupled cavity system
Subjects: Quantum Physics (quant-ph)

We study the photon blockade effect in a coupled cavity system, which is formed by a linear cavity coupled to a Kerr-type nonlinear cavity via a photon-hopping interaction. We explain the physical phenomenon from the viewpoint of the conventional and unconventional photon blockade effects. The corresponding physical mechanisms of these two photon blockade effects are based on the anharmonicity in eigenenergy spectrum and the destructive quantum interference between two different transition paths, respectively. We find that the quantum interference effect also exists in the conventional photon blockade regime. Our results are confirmed by analytically and numerically solving the quantum master equation and calculating the second-order correlation function of the cavity fields. This model is general and hence it can be implemented in various experimental setups such as coupled optical cavities, coupled photon-magnon systems, and coupled superconducting resonators. We present some discussions on the experimental implementation.

[10]
Title: Sub-Riemannian Geodesics on SU(n)/S(U(n-1)xU(1)) and Optimal Control of Three Level Quantum Systems
Subjects: Quantum Physics (quant-ph); Optimization and Control (math.OC)

We study the time optimal control problem for the evolution operator of an n-level quantum system from the identity to any desired final condition. For the considered class of quantum systems the control couples all the energy levels to a given one and is assumed to be bounded in Euclidean norm. From a mathematical perspective, such a problem is a sub-Riemannian K-P problem, whose underlying symmetric space is SU(n)/S(U(n-1) x U(1)). Following the method of symmetry reduction, we consider the action of S(U(n-1) xU(1)) on SU(n) as a conjugation X ---> AXA^{-1}. This allows us to do a symmetry reduction and consider the problem on a quotient space. We give an explicit description of such a quotient space which has the structure of a stratified space. We prove several properties of sub-Riemannian problems with the given structure. We derive the explicit optimal control for the case of three level quantum systems where the desired operation is on the lowest two energy levels (Lambda-systems). We solve this latter problem by reducing it to an integer quadratic optimization problem with linear constraints.

[11]
Title: Controllability of Symmetric Spin Networks
Subjects: Quantum Physics (quant-ph); Optimization and Control (math.OC)

We consider a network of n spin 1/2 systems which are pairwise interacting via Ising interaction and are controlled by the same electro-magnetic control field. Such a system presents symmetries since the Hamiltonian is unchanged if we permute two spins. This prevents full (operator) controllability in that not every unitary evolution can be obtained. We prove however that controllability is verified if we restrict ourselves to unitary evolutions which preserve the above permutation invariance. For low dimensional cases, n=2 and n=3, we provide an analysis of the Lie group of available evolutions and give explicit control laws to transfer between any two permutation invariant states. This class of states includes highly entangled states such as GHZ states and W states, which are of interest in quantum information.

[12]
Title: Excluding joint probabilities from quantum theory
Comments: 5 pages, no figures, Rapid Communication
Journal-ref: Phys. Rev. A 97, 030102(R) (2018)
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Data Analysis, Statistics and Probability (physics.data-an)

Quantum theory does not provide a unique definition for the joint probability of two non-commuting observables, which is the next important question after the Born's probability for a single observable. Instead, various definitions were suggested, e.g. via quasi-probabilities or via hidden-variable theories. After reviewing open issues of the joint probability, we relate it to quantum imprecise probabilities, which are non-contextual and are consistent with all constraints expected from a quantum probability. We study two non-commuting observables in a two-dimensional Hilbert space and show that there is no precise joint probability that applies for any quantum state and is consistent with imprecise probabilities. This contrasts to theorems by Bell and Kochen-Specker that exclude joint probabilities for more than two non-commuting observables, in Hilbert space with dimension larger than two. If measurement contexts are included into the definition, joint probabilities are not anymore excluded, but they are still constrained by imprecise probabilities.

[13]
Title: Melting a Hubbard dimer: benchmarks of ALDA' for quantum thermodynamics
Subjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)

The competition between evolution time, interaction strength, and temperature challenges our understanding of many-body quantum systems out-of-equilibrium. Here we consider a benchmark system, the Hubbard dimer, which allows us to explore all the relevant regimes and calculate exactly the related average quantum work. At difference with previous studies, we focus on the effect of increasing temperature, and show how this can turn competition between many-body interactions and driving field into synergy. We then turn to use recently proposed protocols inspired by density functional theory to explore if these effects could be reproduced by using simple approximations. We find that, up to and including intermediate temperatures, a method which borrows from ground-state adiabatic local density approximation improves dramatically the estimate for the average quantum work, including, in the adiabatic regime, when correlations are strong. However at high temperature and at least when based on the pseudo-LDA, this method fails to capture the counterintuitive qualitative dependence of the quantum work with interaction strength, albeit getting the quantitative estimates relatively close to the exact results.

[14]
Title: Generation and detection of non-Gaussian phonon-added coherent states in optomechanical systems
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)

Adding excitations on a coherent state provides an effective way to observe nonclassical properties of radiation fields. Here we describe and analyse how to apply this concept to the motional state of a mechanical oscillator and present a full scheme to prepare non-Gaussian {\it phonon}-added coherent states of the mechanical motion in cavity optomechanics. We first generate a mechanical coherent state using electromagnetically induced transparency. We then add a single phonon onto the coherent state via optomechanical parametric down-conversion combined with single photon detection. We validate this single-phonon-added coherent state by using a red-detuned beam and reading out the state of the optical output field. This approach allows us to verify nonclassical properties of the phonon state, such as sub-Poissonian character and quadrature squeezing. We further show that our scheme can be directly implemented using existing devices, and is generic in nature and hence applicable to a variety of systems in opto- and electromechanics.

[15]
Title: Comparing and Integrating Constraint Programming and Temporal Planning for Quantum Circuit Compilation
Comments: 9 pages, 2 figures, Proceedings of the 28th International Conference of Automated Planning and Scheduling 2018 (ICAPS-18)
Subjects: Quantum Physics (quant-ph); Artificial Intelligence (cs.AI); Emerging Technologies (cs.ET); Systems and Control (cs.SY)

Recently, the makespan-minimization problem of compiling a general class of quantum algorithms into near-term quantum processors has been introduced to the AI community. The research demonstrated that temporal planning is a strong approach for a class of quantum circuit compilation (QCC) problems. In this paper, we explore the use of constraint programming (CP) as an alternative and complementary approach to temporal planning. We extend previous work by introducing two new problem variations that incorporate important characteristics identified by the quantum computing community. We apply temporal planning and CP to the baseline and extended QCC problems as both stand-alone and hybrid approaches. Our hybrid methods use solutions found by temporal planning to warm start CP, leveraging the ability of the former to find satisficing solutions to problems with a high degree of task optionality, an area that CP typically struggles with. The CP model, benefiting from inferred bounds on planning horizon length and task counts provided by the warm start, is then used to find higher quality solutions. Our empirical evaluation indicates that while stand-alone CP is only competitive for the smallest problems, CP in our hybridization with temporal planning out-performs stand-alone temporal planning in the majority of problem classes.

[16]
Title: Dual-phase-modulated plug-and-play measurement-device-independent continuous-variable quantum key distribution
Subjects: Quantum Physics (quant-ph)

We suggest an improved plug-and-play measurement-device-independent (MDI) continuous-variable quantum key distribution (CVQKD) via the dual-phase modulation (DPM), aiming to solve an implementation problem with no extra performance penalty. The synchronous loophole of different lasers from Alice and Bob can be elegantly eliminated in the plug-and-play configuration, which gives birth to the convenient implementation when comparing to the Gaussian-modulated coherent-state protocol. While the local oscillator (LO) can be locally generated by the trusted part Charlie, the LO-aimed attacks can be accurately detected in the data post-processing. We derive the security bounds of the DPM-based MDI-CVQKD against optimal Gaussian collective attacks. Taking the finite-size effect into account, the secret key rate can be increased due to the fact that almost all raw keys of the MDI-CVQKD system can be fully exploited for the final secret key generation without sacrificing raw keys in parameter estimation. Moreover, we give an experimental concept of the proposed scheme which can be deemed guideline for final implementation.

[17]
Title: Absorption interferometer based on phase modulation
Authors: Miaodi Guo, Xuemei Su
Subjects: Quantum Physics (quant-ph); Optics (physics.optics)

We propose a scheme in which an arbitrary incidence can be made perfectly reflected/transmitted if a phase setup is adjusted under a specific condition. We analyze the intracavity field variation as well as the output field with changing closed-loop phase of atomic system and relative phase of input probe beams. And we obtain the condition for perfect transmitter or reflector. By adjusting two phase setups, the medium absorption and light interference can be controlled so that photon escape from cavity can be modulated, thus the intensity switching based on phase control can be realized. Then based on the transmission/reflection analysis, total absorption of this system can be investigated. Therefore our scheme can be used as an absorption interferometer to explore the optical absorption in some complicated system. The phase delay dependent on phi_1 or phi_2 in output light intensity can be applied in the realization of quantum phase gate and subtle wave filter. And based on this scheme, we implement the state transfer between perfect transmitter/reflector and non-perfect coherent photon absorber via relative-phase modulation.

[18]
Title: Quantifying the effect of interactions in quantum many-body systems
Comments: 24 pages, 8 figures; submission to SciPost
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)

Free fermion systems enjoy a privileged place in physics. With their simple structure they can explain a variety of effects, ranging from insulating and metallic behaviours to superconductivity and the integer quantum Hall effect. Interactions, e.g. in the form of Coulomb repulsion, can dramatically alter this picture by giving rise to emerging physics that may not resemble free fermions. Examples of such phenomena include high-temperature superconductivity, fractional quantum Hall effect, Kondo effect and quantum spin liquids. The non-perturbative behaviour of such systems remains a major obstacle to their theoretical understanding that could unlock further technological applications. Here, we present a pedagogical review of "interaction distance" [Nat. Commun. 8, 14926 (2017)] -- a systematic method that quantifies the effect interactions can have on the energy spectrum and on the quantum correlations of generic many-body systems. In particular, the interaction distance is a diagnostic tool that identifies the emergent physics of interacting systems. We illustrate this method on the simple example of a one-dimensional Fermi-Hubbard dimer.

[19]
Title: Indeterminism in Physics, Classical Chaos and Bohmian Mechanics. Are Real Numbers Really Real?
Authors: Nicolas Gisin
Comments: 7 pages. Presented at the David Bohm Centennial Symposium, London, Octobre 2017
Subjects: Quantum Physics (quant-ph); History and Philosophy of Physics (physics.hist-ph)

It is usual to identify initial conditions of classical dynamical systems with mathematical real numbers. However, almost all real numbers contain an infinite amount of information. Since a finite volume of space can't contain more than a finite amount of information, I argue that the mathematical real numbers are not physically real. Moreover, a better terminology for the so-called real numbers is "random numbers", as their series of bits are truly random. I propose an alternative classical mechanics that uses only finite-information numbers. This alternative classical mechanics is non-deterministic, despite the use of deterministic equations, in a way similar to quantum theory. Interestingly, both alternative classical mechanics and quantum theories can be supplemented by additional variables in such a way that the supplemented theory is deterministic. Most physicists straightforwardly supplement classical theory with real numbers to which they attribute physical existence, while most physicists reject Bohmian mechanics as supplemented quantum theory, arguing that Bohmian positions have no physical reality. I argue that it is more economical and natural to accept non-determinism with potentialities as a real mode of existence, both for classical and quantum physics.

[20]
Title: Revealing memory effects without solving the master equation
Subjects: Quantum Physics (quant-ph)

We study and compare the sensitivity of multiple non-Markovianity indicators for a qubit subjected to general phase-covariant noise. For each of the indicators, we derive analytical conditions to detect the dynamics as non-Markovian. We present these conditions as relations between the time-dependent decay rates for the general open system dynamics and its commutative and unital subclasses. These relations tell directly if the dynamics is non-Markovian w.r.t. each indicator, without the need to explicitly solve the master equation. Moreover, with a shift in perspective, we show that if one assumes only the general form of the master equation, measuring the non-Markovianity indicators gives us directly non-trivial information on the relations between the unknown decay rates.

[21]
Title: Resource theory of non-Markovianity: A thermodynamic perspective
Subjects: Quantum Physics (quant-ph)

We establish the connection between non-Markovianity and negative entropy production rate for various classes of quantum operations. Generalizing the definition of entropy production rate for non-equilibrium case we connect it with the rate of change of free energy of the system and establish complementary relations between non-Markovianity and maximum loss of free energy. We naturally conclude that non-Markovianity, in terms of divisibility breaking is a necessary resource for backflow of other resources like purity or free energy, under corresponding allowed operations. Based on this we propose a resource theory of non-Markovianity by constructing the free operations, free states and a generalized measure of non-Markovianity. The framework satisfies the basic properties of a consistent resource theory. The proposed resource quantifier is lower bounded by the optimization free Rivas-Huelga-Plenio (RHP) measure of non-Markovianity.

[22]
Title: Trade-off Between Work and Correlations in Quantum Thermodynamics
Comments: 10 pages, no figures; Chapter of the upcoming book "Thermodynamics in the Quantum Regime - Recent Progress and Outlook", eds. F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso; comments welcome
Subjects: Quantum Physics (quant-ph)

Quantum thermodynamics and quantum information are two frameworks for employing quantum mechanical systems for practical tasks, exploiting genuine quantum features to obtain advantages with respect to classical implementations. While appearing disconnected at first, the main resources of these frameworks, work and correlations, have a complicated yet interesting relationship that we examine here. We review the role of correlations in quantum thermodynamics, with a particular focus on the conversion of work into correlations. We provide new insights into the fundamental work cost of correlations and the existence of optimally correlating unitaries, and discuss relevant open problems.

[23]
Title: Quantifying coherence with quantum addition
Subjects: Quantum Physics (quant-ph); Information Theory (cs.IT)

Quantum addition channels have been recently introduced in the context of deriving entropic power inequalities for finite dimensional quantum systems. We prove a reverse entropy power equality which can be used to analytically prove an inequality conjectured recently for arbitrary dimension and arbitrary addition weight. We show that the relative entropic difference between the output of such a quantum additon channel and the corresponding classical mixture quantitatively captures the amount of coherence present in a quantum system. This new coherence measure admits an upper bound in terms of the relative entropy of coherence and is utilized to formulate a state-dependent uncertainty relation for two observables. Our results may provide deep insights to the origin of quantum coherence for mixed states that truly come from the discrepancy between quantum addition and the classical mixture.

[24]
Title: Room temperature conditional $π$-phase shifts mediated by simultaneously propagating single-photon level pulses
Subjects: Quantum Physics (quant-ph)

Here we demonstrate the first room-temperature implementation of $\pi$ phase shifts in single-photon-level probe light created by a simultaneously propagating few-photon triggering signal field. The photon-photon interaction is mediated by rubidium atoms in a double $\Lambda$ atomic scheme. We use homodyne tomography and maximum likelihood estimation on the quadrature statistics of the input and phase-shifted photons to fully characterize their quantum states in the Fock state basis. For particular choices in control fields strengths and input phases, the input-output fidelity of the controlled $\pi$ phase shift operation reaches $\sim$90$\%$.

[25]
Title: Two-photon interference in the telecom C-band after frequency conversion of photons from remote quantum emitters
Authors: Jonas H. Weber (1), Benjamin Kambs (2), Jan Kettler (1), Simon Kern (1), Julian Maisch (1), Hüseyin Vural (1), Michael Jetter (1), Simone L. Portalupi (1), Christoph Becher (2), Peter Michler (1) ((1) Institut für Halbleiteroptik und Funktionelle Grenzflächen, Center for Integrated Quantum Science and Technology (IQST) and SCoPE, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany, (2) Fachrichtung Physik, Universität des Saarlandes, Campus E 2.6, 66123 Saarbrücken, Germany)
Comments: J. H. Weber and B. Kambs contributed equally to this work
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Optics (physics.optics)

Efficient fiber-based long-distance quantum communication via quantum repeaters relies on deterministic single-photon sources at telecom wavelengths, with the potential to exploit the existing world-wide infrastructures. For upscaling the experimental complexity in quantum networking, two-photon interference (TPI) of remote non-classical emitters in the low-loss telecom bands is of utmost importance. With respect to TPI of distinct emitters, several experiments have been conducted, e.g., using trapped atoms [Beugnon2006], ions [Maunz2007], NV-centers [Bernien2012, Sipahigil2012], SiV-centers [Sipahigil2014], organic molecules [Lettow2010] and semiconductor quantum dots (QDs) [Patel2010, Flagg2010, He2013b, Gold2014, Giesz2015, Thoma2017, Reindl2017, Zopf2017]; however, the spectral range was far from the highly desirable telecom C-band. Here, we report on TPI at 1550 nm between down-converted single photons from remote QDs [Michler2017Book], demonstrating quantum frequency conversion [Zaske2012, Ates2012, Kambs2016] as precise and stable mechanism to erase the frequency difference between independent emitters. On resonance, a TPI-visibility of (29+-3)% has been observed, being only limited by spectral diffusion processes of the individual QDs [Robinson2000, Kuhlmann2015]. Up to 2-km of additional fiber channel has been introduced in both or individual signal paths with no influence on TPI-visibility, proving negligible photon wave-packet distortion. The present experiment is conducted within a local fiber network covering several rooms between two floors of the building. Our studies pave the way to establish long-distance entanglement distribution between remote solid-state emitters including interfaces with various quantum hybrid systems [DeGreve2012,Maring2017,Bock2017,Maring2018].

[26]
Title: Batched quantum state exponentiation and quantum Hebbian learning
Subjects: Quantum Physics (quant-ph)

Machine learning is a crucial aspect of artificial intelligence. This paper details an approach for quantum Hebbian learning through a batched version of quantum state exponentiation. Here, batches of quantum data are interacted with learning and processing quantum bits (qubits) by a series of elementary controlled partial swap operations, resulting in a Hamiltonian simulation of the statistical ensemble of the data. We decompose this elementary operation into one and two qubit quantum gates from the Clifford+$T$ set and use the decomposition to perform an efficiency analysis. Our construction of quantum Hebbian learning is motivated by extension from the established classical approach, and it can be used to find details about the data such as eigenvalues through phase estimation. This work contributes to the near-term development and implementation of quantum machine learning techniques.

### Cross-lists for Tue, 20 Mar 18

[27]  arXiv:1803.05945 (cross-list from cs.ET) [pdf, other]
Title: Analog simulator of integro-differential equations with classical memristors
Subjects: Emerging Technologies (cs.ET); Neural and Evolutionary Computing (cs.NE); Quantum Physics (quant-ph)

An analog computer makes use of continuously changeable quantities of a system, such as its electrical, mechanical, or hydraulic properties, to solve a given problem. While these devices are usually computationally more powerful than their digital counterparts, they suffer from analog noise which does not allow to error control. We will focus on analog computers based on active electrical networks comprised of resistors, capacitors, and operational amplifiers which are capable of simulating any linear ordinary differential equation. However, the class of nonlinear dynamics they can solve is limited. In this work, by adding memristors to the electrical network, we show that the analog computer can simulate a large variety of linear and nonlinear integro-differential equations by carefully choosing the conductance and the dynamics of the memristor state variable. We study the performance of these analog computers by simulating integro-differential models of fluid dynamics type, nonlinear Volterra equations for population growth, and quantum models describing non-Markovian memory effects, among others. Finally, we perform stability tests by considering imperfect analog components, obtaining robust solutions with up to $13\%$ relative error for relevant timescales.

[28]  arXiv:1803.06338 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Elliptic flow in a strongly-interacting normal Bose gas
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph); Plasma Physics (physics.plasm-ph); Quantum Physics (quant-ph)

We study the anisotropic, elliptic expansion of a thermal atomic Bose gas released from an anisotropic trapping potential, for a wide range of interaction strengths across a Feshbach resonance. We show that in our system this hydrodynamic phenomenon is for all interaction strengths fully described by a microscopic kinetic model with no free parameters. The success of this description crucially relies on taking into account the reduced thermalising power of elastic collisions in a strongly interacting gas, for which we derive an analytical theory. We also perform time-resolved measurements that directly reveal the dynamics of the energy transfer between the different expansion axes.

[29]  arXiv:1803.06426 (cross-list from cond-mat.stat-mech) [pdf, ps, other]
Title: Entanglement in a fermionic spin chain containing a single boson under decoherence
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)

The concurrence between the first and the last parts of a fermionic spin chain containing a single boson is investigated at finite low temperature in the vicinity of a weak homogeneous magnetic field. We consider different positions for the boson in the chain and study concurrence without/under decoherence and express some interesting phase flip and bit flip reactions of the pairwise entanglement between first and the last half-spins of the chain. Our investigations show that the concurrence between two half-spins has different behavior for various positions of the single boson along the chain. Indeed, we realize that the position of the single boson has an essential role to probe the pairwise entanglement between two spins located at the ends of a fermionic chain. Interestingly, the entanglement remains alive for higher temperatures when the boson is adjacent to the first site of the chain.

[30]  arXiv:1803.06462 (cross-list from physics.app-ph) [pdf, other]
Title: 500MHz resonant photodetector for high-frequency, high-quantum-effciency, low-noise homodyne measurement
Subjects: Applied Physics (physics.app-ph); Quantum Physics (quant-ph)

We design and demonstrate a resonant-type differential photodetector, for high-frequency, high-quantum-efficiency, low-noise quantum homodyne measurement at 500MHz optical sideband. By using a microwave monolithic amplifier and a discrete voltage buffer circuit, a low-noise voltage amplifier is realized and applied to our detector. 12dB of signal-to-noise ratio of the shot noise to the electric noise is obtained with 5mW of continuous-wave local oscillator at 860nm. We analyze the frequency response and the noise characteristics of a resonant photodetector, and the theoretical model agrees with the shot noise measurement.

[31]  arXiv:1803.06474 (cross-list from cond-mat.dis-nn) [pdf, ps, other]
Title: Finite-Size Scaling Regarding Interaction in the Many-Body Localization Transition
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)

We present a novel finite-size scaling for both interaction and disorder strengths in the critical regime of the many-body localization (MBL) transition for a spin-1/2 XXZ spin chain with random field by studying the level statistics. We show how the dynamical transition from the thermal to MBL phase depends on interaction together with disorder by evaluating the adjacent gap ratio, and thus, extend previous studies in which the interaction coupling is fixed. We introduce an extra critical exponent in order to describe the nontrivial interaction dependence of the MBL transition. It is characterized by the ratio of the disorder strength to the power of the interaction coupling with respect to the extra critical exponent and not by the simple ratio between them.

[32]  arXiv:1803.06654 (cross-list from cond-mat.supr-con) [pdf, other]
Title: Inelastic scattering of microwave radiation in the Coulomb blockade: Microwave absorption, amplification, and squeezing by inelastic Cooper-pair tunneling
Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We study scattering of propagating microwave fields by a DC-voltage-biased Josephson junction. At sub-gap voltages, a small Josephson junction works merely as a non-linear boundary that can absorb, amplify, and diversely convert propagating microwaves. We find that in the leading-order perturbation theory of the Josephson coupling energy, the spectral density and quadrature fluctuations of scattered thermal and coherent radiation can be described in terms of the well-known $P(E)$ function. Applying this, we show how thermal and coherent radiation can be absorbed and amplified in a circuit with a resonance frequency. We also show when a coherent input can create a two-mode squeezed output. In addition, we evaluate scattering amplitudes between arbitrary photon-number (Fock) states, describing individual photon multiplication and absorption processes occuring at the junction.

[33]  arXiv:1803.06672 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
Title: Topological phases and edge states in a non-Hermitian trimerized optical lattice
Authors: L. Jin
Journal-ref: Physical Review A 96, 032103 (2017)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

Topologically engineered optical materials support robust light transport. Herein, the investigated non-Hermitian lattice is trimerized and inhomogeneously coupled using uniform intracell coupling. The topological properties of the coupled waveguide lattice are evaluated, the PT-symmetric phase of a PT-symmetric lattice can have different topologies; the edge states depend on the lattice size, boundary configuration, and competition between the coupling and degree of non-Hermiticity. The topologically nontrivial region extends in the presence of periodic gain and loss. The nonzero geometric phases accumulated by the Bloch bands indicate the existence of topologically protected edge states between the band gaps. The unidirectional amplification and attenuation zero modes appear above a threshold degree of non-Hermiticity, which facilitate the development of a robust optical diode.

[34]  arXiv:1803.06834 (cross-list from cond-mat.other) [pdf, other]
Title: Ground-state wavefunction of macroscopic electron systems
Authors: Peter Fulde
Subjects: Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)

Wavefunctions for large electron numbers $N$ are plagued by the Exponential Wall Problem (EWP), i.e., an exponential increase in the dimensions of Hilbert space with $N$. Therefore they loose their meaning for macroscopic systems, a point stressed in particular by W. Kohn. The EWP has to be resolved in order to be able to perform electronic structure calculations, e.g., for solids. The origin of the EWP is the multiplicative property of wavefunctions when independent subsystems are considered. Therefore it can only be avoided when wavefunctions are formulated so that they are additive instead, in particular when matrix elements involving them are calculated. We describe how this is done for the ground state of a macroscopic electron system. Going over from a multiplicative to an additive quantity requires taking a logarithm. Here it implies going over from Hilbert space to the operator- or Liouville space with a metric based on cumulants. The operators which define the ground-state wavefunction generate fluctuations from a mean-field state. The latter does not suffer from an EWP and therefore may serve as a vacuum state. The fluctuations have to be {\it connected} like the ones caused by pair interactions in a classical gas when the free energy is calculated (Meyer's cluster expansion). This fixes the metric in Liouville space. The scheme presented here provides a solid basis for electronic structure calculations for the ground state of solids. In fact, its applicability has already been proven. We discuss also matrix product states, which have been applied to one-dimensional systems with results of high precision. Although these states are formulated in Hilbert space they are processed by using operators in Liouville space. We show that they fit into the general formalism described above.

[35]  arXiv:1803.06882 (cross-list from math-ph) [pdf, ps, other]
Title: The correct formulation of Gleason's theorem in quaternionic Hilbert spaces
Authors: Valter Moretti, Marco Oppio (Trento U. and TIFPA-INFN)
Subjects: Mathematical Physics (math-ph); High Energy Physics - Theory (hep-th); Operator Algebras (math.OA); Quantum Physics (quant-ph)

From the viewpoint of the theory of orthomodular lattices of elementary propositions, Quantum Theories can be formulated in real, complex or quaternionic Hilbert spaces as established in Sol\'er's theorem. The said lattice eventually coincides with the lattice of all orthogonal projectors on a separable Hilbert space over R, C, or over the algebra of quaternions H. Quantum states are $\sigma$-additive probability measures on that non-Boolean lattice. Gleason's theorem proves that, if the Hilbert space is separable with dimension >2 and the Hilbert space is either real or complex, then states are one-to-one with standard density matrices (self-adjoint, positive, unit-trace, trace-class operators). The extension of this result to quaternionic Hilbert spaces was obtained by Varadarajan in 1968. Unfortunately, even if the hard part of the proof is correct, the formulation of this extension is mathematically incorrect. This is due to some peculiarities of the notion of trace in quaternionic Hilbert spaces, e.g., basis dependence, making the theory of trace-class operators in quaternionic Hilbert spaces different from the standard theory in real and complex Hilbert spaces. A minor issue also affects Varadarajan's statement for real Hilbert space formulation. This paper is mainly devoted to present Gleason-Varadarajan's theorem into a technically correct form valid for the three types of Hilbert spaces. After having develped part of the general mathematical technology of trace-class operators in (generally non-separable) quaternionic Hilbert spaces, we prove that only the {\em real part} of the trace enters the formalism of quantum theories (also dealing with unbounded observables and symmetries) and it can be safely used to formulate and prove a common statement of Gleason's theorem.

[36]  arXiv:1803.06957 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Quenched dynamics and spin-charge separation in an interacting topological lattice
Comments: 5 pages 3 figures + 2 pages 2 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

We analyze the static and dynamical properties of a one-dimensional topological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence of on-site interactions. Based on a study of charge and spin correlation functions, we elucidate the nature of the topological edge modes, which depending on the sign of the interactions, either display particles of opposite spin on opposite edges, or a pair and a holon. This study of correlation functions also highlights the strong entanglement that exists between the opposite edges of the system. This last feature has remarkable consequences upon subjecting the system to a quench, where an instantaneous edge-to-edge signal appears in the correlation functions characterizing the edge modes. Besides, other correlation functions are shown to propagate in the bulk according to the light-cone imposed by the Lieb-Robinson bound. Our study reveals how one-dimensional lattices exhibiting entangled topological edge modes allow for a non-trivial correlation spreading, while providing an accessible platform to detect spin-charge separation using state-of-the-art experimental techniques.

[37]  arXiv:1803.06987 (cross-list from cs.IT) [pdf, ps, other]
Title: Synthesis of Logical Clifford Operators via Symplectic Geometry
Comments: Single column, main text: 20 pages, full length with appendices: 32 pages. Includes pseudo-codes for all algorithms. Part of this work has been submitted to the 2018 IEEE International Symposium on Information Theory
Subjects: Information Theory (cs.IT); Quantum Physics (quant-ph)

Quantum error-correcting codes can be used to protect qubits involved in quantum computation. This requires that logical operators acting on protected qubits be translated to physical operators (circuits) acting on physical quantum states. We propose a mathematical framework for synthesizing physical circuits that implement logical Clifford operators for stabilizer codes. Circuit synthesis is enabled by representing the desired physical Clifford operator in $\mathbb{C}^{N \times N}$ as a partial $2m \times 2m$ binary symplectic matrix, where $N = 2^m$. We state and prove two theorems that use symplectic transvections to efficiently enumerate all symplectic matrices that satisfy a system of linear equations. As an important corollary of these results, we prove that for an $[\![ m,m-k ]\!]$ stabilizer code every logical Clifford operator has $2^{k(k+1)/2}$ symplectic solutions. The desired physical circuits are then obtained by decomposing each solution as a product of elementary symplectic matrices. Our assembly of the possible physical realizations enables optimization over them with respect to a suitable metric. Furthermore, we show that any circuit that normalizes the stabilizer of the code can be transformed into a circuit that centralizes the stabilizer, while realizing the same logical operation. Our method of circuit synthesis can be applied to any stabilizer code, and this paper provides a proof of concept synthesis of universal Clifford gates for the $[\![ 6,4,2 ]\!]$ CSS code. We conclude with a classical coding-theoretic perspective for constructing logical Pauli operators for CSS codes. Since our circuit synthesis algorithm builds on the logical Pauli operators for the code, this paper provides a complete framework for constructing all logical Clifford operators for CSS codes. Programs implementing our algorithms can be found at https://github.com/nrenga/symplectic-arxiv18a.

[38]  arXiv:1803.07003 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Efficient algorithm to compute the second Chern number in four dimensional systems
Comments: 11 pages, 4 color figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

Topological insulators are exotic material that possess conducting surface states protected by the topology of the system. They can be classified in terms of their properties under discrete symmetries and are characterized by topological invariants. The latter has been measured experimentally for several models in one, two and three dimensions in both condensed matter and quantum simulation platforms. The recent progress in quantum simulation opens the road to the simulation of higher dimensional Hamiltonians and in particular of the 4D quantum Hall effect. These systems are characterized by the second Chern number, a topological invariant that appears in the quantization of the transverse conductivity for the non-linear response to both external magnetic and electric fields. This quantity cannot always be computed analytically and there is therefore a need of an algorithm to compute it numerically. In this work, we propose an efficient algorithm to compute the second Chern number in 4D systems. We construct the algorithm with the help of lattice gauge theory and discuss the convergence to the continuous gauge theory. We benchmark the algorithm on several relevant models, including the 4D Dirac Hamiltonian and the 4D quantum Hall effect and verify numerically its rapid convergence.

### Replacements for Tue, 20 Mar 18

[39]  arXiv:1507.08755 (replaced) [pdf, ps, other]
Title: The Cosmological Constant Problem and Quantum Spacetime Reference Frame
Authors: M.J.Luo
Comments: 15 pages; v4: updated to the published version in IJMPD, interpretation of NLSM being a theory of spacetime reference frame improved, running dimension in renormalization of NLSM and asymptotic safety formally demonstrated, limitations discussed, refs. added
Journal-ref: Int. J. Mod. Phys. D Vol.27(2018)1850081
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
[40]  arXiv:1607.08369 (replaced) [pdf, ps, other]
Title: Probabilistic logic of quantum observations
Subjects: Logic (math.LO); Quantum Physics (quant-ph)
[41]  arXiv:1611.00352 (replaced) [pdf, other]
Title: Device-independent randomness generation from several Bell estimators
Comments: published version (fixed typos; refreshed references) + minor typo fixes
Journal-ref: New J. Phys. 20 (2018) 023049
Subjects: Quantum Physics (quant-ph)
[42]  arXiv:1702.03905 (replaced) [pdf, ps, other]
Title: Quantum principle of sensing gravitational waves: From the zero-point fluctuations to the cosmological stochastic background of spacetime
Comments: 14 pages, 4 figures, with typo corrections
Journal-ref: Phys. Rev. D 96, 044018 (2017)
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Quantum Physics (quant-ph)
[43]  arXiv:1703.03820 (replaced) [pdf, other]
Title: Supersymmetry Breaking at Finite Temperature in a Susy Harmonic Oscillator with Interaction
Comments: 4 pages, 1 figure. arXiv admin note: text overlap with arXiv:cond-mat/0006315 by other authors
Subjects: Quantum Physics (quant-ph)
[44]  arXiv:1705.11036 (replaced) [pdf, ps, other]
Title: Quantum walk on a chimera graph
Subjects: Quantum Physics (quant-ph)
[45]  arXiv:1707.04963 (replaced) [pdf, other]
Title: A large class of solvable multistate Landau-Zener models and quantum integrability
Comments: The 2nd version contains considerable changes, including new sections, that are based on recent advances in arXiv/1711.09945 (new Ref.[1])
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph)
[46]  arXiv:1707.08963 (replaced) [pdf, other]
Title: Universal quantum uncertainty relations between non-ergodicity and loss of information
Journal-ref: Phys. Rev. A 97, 032103 (2018)
Subjects: Quantum Physics (quant-ph)
[47]  arXiv:1708.02487 (replaced) [pdf, ps, other]
Title: Spectral density of mixtures of random density matrices for qubits
Comments: 21 pages, LaTex, 6 figures
Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph)
[48]  arXiv:1708.05627 (replaced) [pdf, other]
Title: Fault-tolerant quantum computation with non-deterministic entangling gates
Journal-ref: Phys. Rev. A 97, 030301 (2018)
Subjects: Quantum Physics (quant-ph)
[49]  arXiv:1708.09757 (replaced) [pdf, other]
Title: Opportunities and challenges for quantum-assisted machine learning in near-term quantum computers
Comments: Contribution to the special issue of Quantum Science & Technology (QST) on "What would you do with 1000 qubits"
Subjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET)
[50]  arXiv:1708.09784 (replaced) [pdf, other]
Title: Quantum-assisted Helmholtz machines: A quantum-classical deep learning framework for industrial datasets in near-term devices
Comments: 11 pages, 2 figures. Minor revisions
Subjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET)
[51]  arXiv:1709.03704 (replaced) [pdf, other]
Title: Full-Counting Many-Particle Dynamics: Nonlocal and Chiral Propagation of Correlations
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
[52]  arXiv:1710.07591 (replaced) [pdf, other]
Title: Characterization of the hyperfine interaction of the excited $^5$D$_0$ state of Eu$^{3+}$:Y$_2$SiO$_5$
Journal-ref: Phys. Rev. B 97, 094416 (2018)
Subjects: Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph)
[53]  arXiv:1710.09174 (replaced) [pdf, other]
Title: Casimir self-stress in a dielectric sphere
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[54]  arXiv:1711.02323 (replaced) [pdf, ps, other]
Title: Characterizing nonclassical correlations via local quantum Fisher information
Journal-ref: Phys. Rev. A 97, 032326 (2018)
Subjects: Quantum Physics (quant-ph)
[55]  arXiv:1711.05450 (replaced) [pdf, ps, other]
Title: Scattering Theory and $\mathcal{P}\mathcal{T}$-Symmetry
Comments: Slightly expanded revised version, 38 pages
Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Optics (physics.optics)
[56]  arXiv:1711.06140 (replaced) [pdf, ps, other]
Title: Generalized speed and cost rate in transitionless quantum driving
Journal-ref: Phys. Rev. A 97, 032115 (2018)
Subjects: Quantum Physics (quant-ph)
[57]  arXiv:1711.10240 (replaced) [pdf, other]
Title: Test one to test many: a unified approach to quantum benchmarks
Comments: 18 pages, 6 figures, typos and grammatical errors fixed
Subjects: Quantum Physics (quant-ph)
[58]  arXiv:1712.04780 (replaced) [pdf, ps, other]
Title: Laser beam scintillations for weak and moderate turbulence
Subjects: Quantum Physics (quant-ph)
[59]  arXiv:1712.08275 (replaced) [pdf, ps, other]
Title: Ultracold anions for high-precision antihydrogen experiments
Subjects: Atomic Physics (physics.atom-ph); Optics (physics.optics); Quantum Physics (quant-ph)
[60]  arXiv:1801.02295 (replaced) [pdf, other]
Title: Interatomic interaction effects on second-order momentum correlations and Hong-Ou-Mandel interference of double-well-trapped ultracold fermionic atoms
Comments: 18 pages, 8 color figures. A new section V was added; it describes entanglement aspects and the connection to the Hong-Ou-Mandel interference physics. Also the whole range for both repulsive and attractive interparticle interaction is now investigated. For related papers, see this http URL
Subjects: Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
[61]  arXiv:1801.02820 (replaced) [pdf, other]
Title: Work production of quantum rotor engines
Comments: 22 pages, 9 figures, accepted version, added reference to L\"orch et al, 1802.10572
Subjects: Quantum Physics (quant-ph)
[62]  arXiv:1801.03782 (replaced) [pdf, other]
Title: 16-qubit IBM universal quantum computer can be fully entangled
Comments: 7 pages, 13 figures; The full entanglement is clarified; a new section is added on the localized entanglement with distance 3 and 4
Subjects: Quantum Physics (quant-ph)
[63]  arXiv:1801.06706 (replaced) [pdf, other]
Title: One way quantum repeaters with quantum Reed-Solomon codes
Subjects: Quantum Physics (quant-ph)
[64]  arXiv:1802.00160 (replaced) [pdf, ps, other]
Title: Bipartite discrimination of independently prepared quantum states as a counterexample of a parallel repetition conjecture
Comments: In this version, we improve a proof of theorem 2
Subjects: Quantum Physics (quant-ph); Computational Complexity (cs.CC)
[65]  arXiv:1802.02010 (replaced) [pdf, ps, other]
Title: Effects of interaction imbalance in a strongly repulsive one-dimensional Bose gas
Journal-ref: Few-Body Syst (2018) 59: 22
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
[66]  arXiv:1802.07419 (replaced) [pdf, other]
Title: Approximate low-weight check codes and circuit lower bounds for noisy ground states
Comments: 32 pages. Version 2 fixes an incorrect statement in equation (39) of Version 1. The statement of the theorem still holds
Subjects: Quantum Physics (quant-ph)
[67]  arXiv:1802.08696 (replaced) [pdf, other]
Title: Correlation functions of the quantum sine-Gordon model in and out of equilibrium
Comments: Animation of quench dynamics in ancillary material: this https URL Version 2: improved presentation
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
[68]  arXiv:1803.02561 (replaced) [pdf, other]
Title: Theory on the optical spinpolarization loop of the nitrogen-vacancy center in diamond
Comments: 13 pages, 6 figures, 1 table
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[69]  arXiv:1803.04023 (replaced) [pdf, ps, other]
Title: A $ψ$-Ontology Result without the Cartesian Product Assumption
Authors: Wayne C. Myrvold
Comments: This version considerable strengthens the result in v1
Subjects: Quantum Physics (quant-ph)
[70]  arXiv:1803.04913 (replaced) [pdf, other]
Title: On non-commutativity in quantum theory (I): from classical to quantum probability
Authors: Luca Curcuraci
Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Probability (math.PR)
[71]  arXiv:1803.04916 (replaced) [pdf, other]
Title: On non-commutativity in quantum theory (II): toy models for non-commutative kinematics
Authors: Luca Curcuraci
Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph); Probability (math.PR)
[72]  arXiv:1803.04921 (replaced) [pdf, other]
Title: On non-commutativity in quantum theory (III): determinantal point processes and non-relativistic quantum mechanics
Authors: Luca Curcuraci