# Quantum Physics

## New submissions

[ total of 45 entries: 1-45 ]
[ showing up to 2000 entries per page: fewer | more ]

### New submissions for Fri, 22 Jun 18

[1]
Title: Quantum state merging for arbitrarily-small-dimensional systems
Comments: 15 pages, 2 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible
Subjects: Quantum Physics (quant-ph)

Quantum technology in the near future will facilitate information processing using quantum computers on the small and intermediate scale of up to several dozens of qubits. We investigate entanglement cost required for one-shot quantum state merging, aiming at quantum state transformation on this scale. In contrast to existing coding algorithms achieving nearly optimal approximate quantum state merging on a large scale, we construct algorithms for exact quantum state merging so that the algorithms are applicable to any given state of an arbitrarily-small-dimensional system. In the algorithms, entanglement cost can be reduced depending on a structure of the given state derived from the Koashi-Imoto decomposition. We also provide an improved converse bound for exact quantum state merging achievable for qubits. Our results are applicable to distributed quantum information processing and multipartite entanglement transformation on a small and intermediate scale.

[2]
Title: Plug-and-Play Approach to Non-adiabatic Geometric Quantum Computation
Subjects: Quantum Physics (quant-ph)

Geometrical phases acquired in cyclic quantum evolutions can be utilized as natural resources for construct- ing robust logic gates for quantum information processing, which was originally proposed through adiabatic changes of the driving Hamiltonian. Practically, much efforts have been made to shorten the construction times of geometrical gates, known as non-adiabatic holonomic quantum computation (NHQC). However, previous NHQC gates require the driving Hamiltonian to satisfy a set of rather restrictive conditions, reducing the robust- ness of the resulting geometric gates against control errors. Here we show that non-adiabatic geometric gates can be constructed in an alternative way where the driving Hamiltonian can exhibit a high degree of flexibility for retaining the robustness of the geometric phases. Consequently, this approach makes it possible to incorporate most of the existing optimal control methods, such as dynamical decoupling, composite pulses, and shortcut to adiabaticity, into the construction of geometrical gates, to further address different types of errors. Furthermore, this extensible approach of geometric quantum computation can be applied to various physical platform such as superconducting qubits and nitrogen-vacancy (NV) centers. Specifically, we performed numerical simulation to show how the noise robustness in the recent experimental implementations [Phys. Rev. Lett. 119, 140503 (2017)] and [Nat. Photonics 11, 309 (2017)] of NHQC with NV centers can be significantly improved by our optimized NHQC approach. These results cover a large class of new techniques combing the noise robustness of both geometric phase and optimal control theory.

[3]
Title: There Is No Action at a Distance in Quantum Mechanics, Spooky or Otherwise
Authors: Stephen Boughn
Subjects: Quantum Physics (quant-ph); History and Philosophy of Physics (physics.hist-ph)

I feel compelled to respond to the frequent references to spooky action at a distance that often accompany reports of experiments investigating entangled quantum mechanical states. Most, but not all, of these articles have appeared in the popular press. As an experimentalist I have great admiration for such experiments and the concomitant advances in quantum information and quantum computing, but accompanying claims of action at a distance are quite simply nonsense. Some physicists and philosophers of science have bought into the story by promoting the nonlocal nature of quantum mechanics. In 1964, John Bell proved that classical hidden variable theories cannot reproduce the predictions of quantum mechanics unless they employ some type of action at a distance. I have no problem with this conclusion. Unfortunately, Bell later expanded his analysis and mistakenly deduced that quantum mechanics and by implication nature herself are nonlocal. In addition, some of these articles present Einstein in caricature, a tragic figure who neither understood quantum mechanics nor believed it to be an accurate theory of nature. Consequently, the current experiments have proven him wrong. This is also nonsense.

[4]
Title: Digital coherent control of a superconducting qubit
Comments: 13 pages, 9 figures, 1 table
Subjects: Quantum Physics (quant-ph); Superconductivity (cond-mat.supr-con)

High-fidelity gate operations are essential to the realization of a fault-tolerant quantum computer. In addition, the physical resources required to implement gates must scale efficiently with system size. A longstanding goal of the superconducting qubit community is the tight integration of a superconducting quantum circuit with a proximal classical cryogenic control system. Here we implement coherent control of a superconducting transmon qubit using a Single Flux Quantum (SFQ) pulse driver cofabricated on the qubit chip. The pulse driver delivers trains of quantized flux pulses to the qubit through a weak capacitive coupling; coherent rotations of the qubit state are realized when the pulse-to-pulse timing is matched to a multiple of the qubit oscillation period. We measure the fidelity of SFQ-based gates to be ~95% using interleaved randomized benchmarking. Gate fidelities are limited by quasiparticle generation in the dissipative SFQ driver. We characterize the dissipative and dispersive contributions of the quasiparticle admittance and discuss mitigation strategies to suppress quasiparticle poisoning. These results open the door to integration of large-scale superconducting qubit arrays with SFQ control elements for low-latency feedback and stabilization.

[5]
Title: Full characterization of a high-dimensional quantum communication channel
Subjects: Quantum Physics (quant-ph); Optics (physics.optics)

The characterization of quantum processes, e.g. communication channels, is an essential ingredient for establishing quantum information systems. For quantum key distribution protocols, the amount of overall noise in the channel determines the rate at which secret bits are distributed between authorized partners. In particular, tomographic protocols allow for the full reconstruction, and thus characterization, of the channel. Here, we perform quantum process tomography of high-dimensional quantum communication channels with dimensions ranging from 2 to 5. We can thus explicitly demonstrate the effect of an eavesdropper performing an optimal cloning attack or an intercept-resend attack during a quantum cryptographic protocol. Our study shows that the process matrix enables a more detailed understanding of the channel conditions compared to a coarse-grained measure, such as quantum bit error rates. This full characterization technique allows us to distinguish eavesdropping attempts and optimize the quantum key distribution performance under asymmetric experimental conditions.

[6]
Title: Modular-value-based metrology with spin coherent pointers
Subjects: Quantum Physics (quant-ph)

Modular values are quantities that described by pre- and postselected states of quantum systems like weak values but are different from them: The associated interaction is not necessary to be weak. We discuss an optimal modular-value-based measurement with a spin coherent pointer: A quantum system is exposed to a field in which strength is to be estimated through its modular value. We consider two cases, with a two-dimensional and a higher-dimensional pointer, and evaluate the quantum Fisher information. The modular-value-based measurement has no merit in the former case, while its sensitivity can be enhanced in the latter case. We also consider the pointer under a phase-flip error. Our study should motivate researchers to apply the modular-value-based measurements for quantum metrology.

[7]
Title: Experimental quantification of spatial correlations in quantum dynamics
Subjects: Quantum Physics (quant-ph)

Correlations between different partitions of quantum systems play a central role in a variety of many-body quantum systems, and they have been studied exhaustively in experimental and theoretical research. Here, we investigate dynamical correlations in the time evolution of multiple parts of a composite quantum system. A rigorous measure to quantify correlations in quantum dynamics based on a full tomographic reconstruction of the quantum process has been introduced recently [\'A. Rivas et al., New Journal of Physics, 17(6) 062001 (2015).]. In this work, we derive a lower bound for this correlation measure, which does not require full knowledge of the quantum dynamics. Furthermore we also extend the correlation measure to multipartite systems. We directly apply the developed methods to a trapped ion quantum information processor to experimentally characterize the correlations in quantum dynamics for two- and four-qubit systems. The method proposed and demonstrated in this work is scalable, platform-independent and applicable to other composite quantum systems and quantum information processing architectures. We apply the method to estimate spatial correlations in environmental noise processes, which are crucial for the performance of quantum error correction procedures.

[8]
Title: Violation of all the second laws of thermal operations by inhomogeneous reservoirs
Subjects: Quantum Physics (quant-ph)

In the resource theory of thermodynamics, the decrease of the free energy based on von Neumann entropy is not a sufficient condition to determine free evolution. Rather, a whole family of generalised free energies $F_{\alpha}$ must be monotonically decreasing. We study the resilience of this result to relaxations of the framework. We use a toy collisional model, in which the deviations from the ideal situation can be described as arising from inhomogeneities of local fields or temperatures. For any small amount of perturbation, we find that there exist initial states such that both single-shot and averaged values of $F_{\alpha}$ do not decrease monotonically for all $\alpha>0$. A geometric representation accounts for the observed behavior in a graphic way.

[9]
Title: High fidelity quantum cloning of two known nonorthogonal quantum states via weak measurement
Subjects: Quantum Physics (quant-ph)

We propose a scheme to enhance the fidelity of symmetric quantum cloning machine using a weak measurement. By adjusting the intensity of weak measurement parameter $p$, we obtain the copies with different optimal fidelity. Choosing proper value of $p$, we can obtain the perfect copies for initial qubits. In this paper, we focus on $1-2$ quantum cloning for two nonorthogonal states. Sets containing more than two linear independent states are also discussed briefly. Due to weak measurements being probabilistic, we obtain high fidelity at risk of probability. If the weak measurement successes, we do the following operations to obtain copies with high fidelity, otherwise, the cloning process fails and we need do nothing. From this perspective, the scheme we propose is economical for saving quantum resource and time, which may be very useful in quantum information processing.

[10]
Title: Uncertainty principle as post-quantum nonlocality witness for continuous variable multi-mode scenario
Subjects: Quantum Physics (quant-ph)

Uncertainty principle is one of the central concepts in quantum theory. Different forms of this particular principle have been discoursed in various foundational and information theoretic topics. In the discrete input-output scenario the limited nonlocal behavior of quantum theory has been explained by fine-grained uncertainty relation. On the other hand, in continuous variable paradigm Robertson-Schrodinger (RS) uncertainty relation has been used to detect multi-mode entanglement. Here we show that RS uncertainty relation plays an important role to discriminate between quantum and post-quantum nonlocal correlations in multi-mode continuous outcome scenario. We provide a class of m-mode post-quantum nonlocal correlations with continuous outcome spectrum. While nonlocality of the introduced class of correlations is established through Calvalcanti-Foster-Reid-Drummond (CFRD) class of Bell inequalities, RS uncertainty relation detects their post-quantum nature. Our result is a hint towards a wider role of uncertainty principle in the study of nonlocality in continuous variable multi-mode systems.

[11]
Title: The notion of locality in relational quantum mechanics
Subjects: Quantum Physics (quant-ph); History and Philosophy of Physics (physics.hist-ph)

The term 'locality' is used in different contexts with different meanings. There have been claims that relational quantum mechanics is local, but it is not clear then how it accounts for the effects that go under the usual name of quantum non-locality. The present article shows that the failure of 'locality' in the sense of Bell, once interpreted in the relational framework, reduces to the existence of a common cause in an indeterministic context. In particular, there is no need to appeal to a mysterious space-like influence to understand it.

[12]
Title: Thermodynamic consistency of the optomechanical master equation
Subjects: Quantum Physics (quant-ph)

We investigate the thermodynamic consistency of the master equation description of heat transport through an optomechanical system attached to two heat baths, one optical and one mechanical. We employ three different master equations to describe this scenario: (i) The standard master equation used in optomechanics, where each bath acts only on the resonator that it is physically connected to; (ii) the so-called dressed-state master equation, where the mechanical bath acts on the global system; and (iii) what we call the global master equation, where both baths are treated non-locally and affect both the optical and mechanical subsystems. Our main contribution is to demonstrate that, under certain conditions including when the optomechanical coupling strength is weak, the second law of thermodynamics is violated by the first two of these pictures. In order to have a thermodynamically consistent description of an optomechanical system, therefore, one has to employ a global description of the effect of the baths on the system.

[13]
Title: Limitations on the indistinguishability of photons from remote solid state sources
Subjects: Quantum Physics (quant-ph)

In the present work, we derive a formalism that can be used to predict and interpret the time structure and achievable visibilities for two-photon interference (TPI) experiments using photons from two separate sources. The treatment particularly addresses photons stemming from solid state quantum emitters, which are often subject to pure dephasing (PD) and spectral diffusion (SD). Therefore, it includes the impact of phase- and emission frequency-jitter besides the influence of differing radiative lifetimes and a relative spectral detuning. While the treatment is mainly aimed at interference experiments after Hong-Ou-Mandel (HOM), we additionally offer generalized equations that are applicable to arbitrary linear optical gates, which rely on TPI.

[14]
Title: Watching the precession of a single nuclear spin by weak measurements
Comments: 8 pages + 22 pages of supplementary material
Subjects: Quantum Physics (quant-ph)

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analyzing the structure and function of molecules, and for performing three-dimensional imaging of the spin density. At the heart of NMR spectrometers is the detection of electromagnetic radiation, in the form of a free induction decay (FID) signal, generated by nuclei precessing around an applied magnetic field. While conventional NMR requires signals from 1e12 or more nuclei, recent advances in sensitive magnetometry have dramatically lowered this number to a level where few or even individual nuclear spins can be detected. It is natural to ask whether continuous FID detection can still be applied at the single spin level, or whether quantum back-action modifies or even suppresses the NMR response. Here we report on tracking of single nuclear spin precession using periodic weak measurements. Our experimental system consists of a 13C nuclear spin in diamond that is weakly interacting with the electronic spin of a nearby nitrogen-vacancy center, acting as an optically readable meter qubit. We observe and minimize two important effects of quantum back-action: Measurement-induced decoherence and frequency synchronization with the sampling clock. We use weak measurements to demonstrate nanoscale NMR spectroscopy with a simultaneous enhancement of the signal-to-noise ratio (SNR), frequency bandwidth and spectral resolution. Our method may provide the optimum route for performing single-molecule NMR at atomic resolution.

[15]
Title: Quantum Kitchen Sinks: An algorithm for machine learning on near-term quantum computers
Authors: C. M. Wilson (Rigetti Computing, Institute for Quantum Computing, University of Waterloo) J. S. Otterbach (Rigetti Computing), N. Tezak (Rigetti Computing), R. S. Smith (Rigetti Computing), G. E. Crooks (Rigetti Computing), M. P. da Silva (Rigetti Computing)
Subjects: Quantum Physics (quant-ph)

Noisy intermediate-scale quantum computing devices are an exciting platform for the exploration of the power of near-term quantum applications. Performing nontrivial tasks in such a framework requires a fundamentally different approach than what would be used on an error-corrected quantum computer. One such approach is to use hybrid algorithms, where problems are reduced to a parameterized quantum circuit that is often optimized in a classical feedback loop. Here we described one such hybrid algorithm for machine learning tasks by building upon the classical algorithm known as random kitchen sinks. Our technique, called quantum kitchen sinks, uses quantum circuits to nonlinearly transform classical inputs into features that can then be used in a number of machine learning algorithms. We demonstrate the power and flexibility of this proposal by using it to solve binary classification problems for synthetic datasets as well as handwritten digits from the MNIST database. We can show, in particular, that small quantum circuits provide significant performance lift over standard linear classical algorithms, reducing classification error rates from $50\%$ to $<0.1\%$, and from $4.1\%$ to $1.4\%$ in these two examples, respectively.

[16]
Title: Quantum thermodynamics with multiple conserved quantities
Comments: 18 pages, 3 figures; Chapter for the book "Thermodynamics in the Quantum Regime - Recent Progress and Outlook", eds. F. Binder, L. A. Correa, C. Gogolin, J. Anders and G. Adesso
Subjects: Quantum Physics (quant-ph)

In this chapter we address the topic of quantum thermodynamics in the presence of additional observables beyond the energy of the system. In particular we discuss the special role that the generalized Gibbs ensemble plays in this theory, and derive this state from the perspectives of a micro-canonical ensemble, dynamical typicality and a resource-theory formulation. A notable obstacle occurs when some of the observables do not commute, and so it is impossible for the observables to simultaneously take on sharp microscopic values. We show how this can be circumvented, discuss information-theoretic aspects of the setting, and explain how thermodynamic costs can be traded between the different observables. Finally, we discuss open problems and future directions for the topic.

[17]
Title: Dephrasure channel and superadditivity of coherent information
Subjects: Quantum Physics (quant-ph)

The quantum capacity of a quantum channel captures its capability for noiseless quantum communication. It lies at the heart of quantum information theory. Unfortunately, our poor understanding of nonadditivity of coherent information makes it hard to understand the quantum capacity of all but very special channels. In this paper, we consider the dephrasure channel, which is the concatenation of a dephasing channel and an erasure channel. This very simple channel displays remarkably rich and exotic properties: we find nonadditivity of coherent information at the two-letter level, a substantial gap between the threshold for zero quantum capacity and zero single-letter coherent information, a big gap between single-letter coherent and private informations. Its clean form simplifies the evaluation of coherent information substantially and, as such, we hope that the dephrasure channel will provide a much-needed laboratory for the testing of new ideas about nonadditivity.

### Cross-lists for Fri, 22 Jun 18

[18]  arXiv:1806.07456 (cross-list from eess.SP) [pdf, other]
Title: Turbulence correction with artificial neural networks
Comments: 4 pages, 4 figures, 1 table
Journal-ref: Optics Letters Vol. 43, Issue 11, pp. 2611-2614 (2018)
Subjects: Signal Processing (eess.SP); Optics (physics.optics); Quantum Physics (quant-ph)

We design an optical feedback network making use of machine learning techniques and demonstrate via simulations its ability to correct for the effects of turbulent propagation on optical modes. This artificial neural network scheme only relies on measuring the intensity profile of the distorted modes, making the approach simple and robust. The network results in the generation of various mode profiles at the transmitter that, after propagation through turbulence, closely resemble the desired target mode. The corrected optical mode profiles at the receiver are found to be nearly identical to the desired profiles, with near-zero mean square error indices. We are hopeful that the present results combining the fields of machine learning and optical communications will greatly enhance the robustness of free-space optical links.

[19]  arXiv:1806.07661 (cross-list from physics.optics) [pdf]
Title: Super-resolution enhancement by quantum image scanning microscopy
Subjects: Optics (physics.optics); Quantum Physics (quant-ph)

The principles of quantum optics have yielded a plethora of ideas to surpass the classical limitations of sensitivity and resolution in optical microscopy. While some ideas have been applied in proof-of-principle experiments, imaging a biological sample has remained challenging mainly due to the inherently weak signal measured and the fragility of quantum states of light. In principle, however, these quantum protocols can add new information without sacrificing the classical information and can therefore enhance the capabilities of existing super-resolution techniques. Image scanning microscopy (ISM), a recent addition to the family of super-resolution methods, generates a robust resolution enhancement without sacrificing the signal level. Here we introduce quantum image scanning microscopy (Q-ISM): combining ISM with the measurement of quantum photon correlation allows increasing the resolution of ISM up to two-fold, four times beyond the diffraction limit. We introduce the Q-ISM principle and obtain super-resolved optical images of a biological sample stained with fluorescent quantum dots using photon antibunching, a quantum effect, as a resolution enhancing contrast mechanism.

[20]  arXiv:1806.07960 (cross-list from math.CA) [pdf]
Title: Series solutions of Heun-type equation in terms of orthogonal polynomials
Authors: A. D. Alhaidari
Subjects: Classical Analysis and ODEs (math.CA); Mathematical Physics (math-ph); Quantum Physics (quant-ph)

We introduce a nine-parameter Heun-type differential equation and obtain three classes of its solutions as series of square integrable functions written in terms of the Jacobi polynomial. The expansion coefficients of the series satisfy three-term recursion relations, which are solved in terms of orthogonal polynomials with continuous and/or discrete spectra. Some of these are well-known polynomials while others are either new or modified versions of known ones.

[21]  arXiv:1806.08043 (cross-list from gr-qc) [pdf, other]
Title: Structure of Correlated Worldline Theories of Quantum Gravity
Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)

We consider the general form of "Correlated Worldline" (CWL) theories of quantum gravity. We show that one can have 2 different kinds of CWL theory, in which the generating functional is written as either a sum or a product over multiple copies of the coupled matter and gravitational fields. In both versions, the paths in a functional formulation are correlated via gravity itself, causing a breakdown of the superposition principle; however, the product form survives consistency tests not satisfied by the summed form. To better understand the structure of these two theories, we show how to perform diagrammatic expansions in the gravitational coupling for each version of CWL theory, using particle propagation and scalar fields as examples. We explicitly calculate contributions to 2-point and 4-point functions, again for each version of the theory, up to 2nd-order in the gravitational coupling.

[22]  arXiv:1806.08060 (cross-list from cond-mat.str-el) [pdf, ps, other]
Title: Reconstructing Entanglement Hamiltonian via Entanglement Eigenstates
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)

The entanglement Hamiltonian $H_E$, defined through the reduced density matrix of a subsystem $\rho_A=\exp(-H_E)$, is an important concept in understanding the nature of quantum entanglement in many-body systems and quantum field theories. In this work, we explore a numerical scheme which explicitly reconstructs the entanglement Hamiltonian using one entangled mode (i.e., an eigenstate) of $\rho_A$. We demonstrate and benchmark this scheme on quantum spin lattice models. The resulting $H_E$ bears a form similar to a physical Hamiltonian with spatially varying couplings, which allows us to make quantitative comparison with perturbation theory and conformal field theory.

[23]  arXiv:1806.08171 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Measuring the single-particle density matrix for fermions and hard-core bosons in an optical lattice
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

Ultracold atoms in optical lattices provide clean, tunable, and well-isolated realizations of paradigmatic quantum lattice models. With the recent advent of quantum-gas microscopes, they now also offer the possibility to measure the occupations of individual lattice sites. What, however, has not yet been achieved is to measure those elements of the single-particle density matrix, which are off-diagonal in the occupation basis. Here, we propose a scheme to access these basic quantities both for fermions as well as hard-core bosons and investigate its accuracy and feasibility. The scheme relies on the engineering of a large effective tunnel coupling between distant lattice sites and a protocol that is based on measuring site occupations after two subsequent quenches.

[24]  arXiv:1806.08191 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
Title: Dynamically Generated Synthetic Electric Fields for Photons
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

Static synthetic magnetic fields give rise to phenomena including the Lorentz force and the quantum Hall effect even for neutral particles, and they have by now been implemented in a variety of physical systems. Moving towards fully dynamical synthetic gauge fields allows, in addition, for backaction of the particles' motion onto the field. If this results in a time-dependent vector potential, conventional electromagnetism predicts the generation of an electric field. Here, we show how synthetic electric fields for photons arise self-consistently due to the nonlinear dynamics in a driven system. Our analysis is based on optomechanical arrays, where dynamical gauge fields arise naturally from phonon-assisted photon tunneling. We study open, one-dimensional arrays, where synthetic magnetic fields are absent. However, we show that synthetic electric fields can be generated dynamically, which, importantly, suppress photon transport in the array. The generation of these fields depends on the direction of photon propagation, leading to a novel mechanism for a photon diode, inducing nonlinear nonreciprocal transport via dynamical synthetic gauge fields.

[25]  arXiv:1806.08227 (cross-list from math.LO) [pdf, ps, other]
Title: The assumption of the Hilbert lattice in the case of a two-dimensional system
Subjects: Logic (math.LO); Quantum Physics (quant-ph)

As it is known, the set of all closed linear subspaces of a Hilbert space together with a binary relation over the set represents the logic of the quantum propositions. It is also known that the lattices of the closed linear subspaces on a Hilbert space of dimension 3 or greater do not have a prime filter, hence those lattices do not allow a valuation map. In contrast to that, for qubits it is easy to find prime filters in the Hilbert lattice. This begs the question: What assumption(s) related to the lattices of the closed linear subspaces should be added or altered to preclude the bivaluation map in the two-dimensional case? The presented paper offers the answer to this question.

[26]  arXiv:1806.08285 (cross-list from physics.optics) [pdf, other]
Title: Photons in the presence of parabolic mirrors
Subjects: Optics (physics.optics); Quantum Physics (quant-ph)

We present a vectorial analysis of the behavior of the electromagnetic field in the presence of boundaries with parabolic geometry. The relevance of the use of symmetries to find explicit closed expressions for the electromagnetic fields is emphasized. Polarization and phase related angular momenta of light have an essential role in the proper definition of the generator $\mathfrak{A}_3$ of a symmetry transformation that distinguishes the parabolic geometry. Quantization of the electromagnetic field in terms of the resulting elementary modes is performed. The important case of a boundary defined by an ideal parabolic mirror is explicitly worked out. The presence of the mirror restricts the eigenvalues of $\mathfrak{A}_3$ available to the electric and magnetic fields of a given mode via compact expressions. Modes previously reported in the literature are particular cases of those described in this work.

[27]  arXiv:1806.08316 (cross-list from cond-mat.dis-nn) [pdf, other]
Title: Detection and characterization of Many-Body Localization in Central Spin Models
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)

We analyze a disordered central spin model, where a central spin interacts equally with each spin in a periodic one dimensional random-field Heisenberg chain. If the Heisenberg chain is initially in the many-body localized (MBL) phase, we find that the coupling to the central spin suffices to delocalize the chain for a substantial range of coupling strengths. We calculate the phase diagram of the model and identify the phase boundary between the MBL and ergodic phase. Within the localized phase, the central spin significantly enhances the rate of the logarithmic entanglement growth and its saturation value. We attribute the increase in entanglement entropy to a non-extensive enhancement of magnetization fluctuations induced by the central spin. Finally, we demonstrate that correlation functions of the central spin can be utilized to distinguish between MBL and ergodic phases of the 1D chain. Hence, we propose the use of a central spin as a possible experimental probe to identify the MBL phase.

### Replacements for Fri, 22 Jun 18

[28]  arXiv:1608.04722 (replaced) [pdf, other]
Title: Pretty Good State Transfer in Qubit Chains - The Heisenberg Hamiltonian
Comments: The first version of this paper made available on Arxiv contained the false claim that pretty good state transfer occurs between end vertices in a path of length $n$ where $n$ is a prime congruent to $1$ modulo $4$. This claim has been corrected in this version
Subjects: Quantum Physics (quant-ph); Combinatorics (math.CO)
[29]  arXiv:1611.05127 (replaced) [pdf]
Title: Quantized Ballistic Transport of Electrons and Electron Pairs in LaAlO$_3$/SrTiO$_3$ Nanowires
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
[30]  arXiv:1705.04472 (replaced) [pdf, other]
Title: Nonclassical light from large ensemble of trapped ions
Journal-ref: Phys. Rev. Lett. 120, 253602 (2018)
Subjects: Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph)
[31]  arXiv:1706.03828 (replaced) [pdf, other]
Title: Quantification and manipulation of magic states
Journal-ref: Phys. Rev. A 97, 062332 (2018)
Subjects: Quantum Physics (quant-ph)
[32]  arXiv:1707.09722 (replaced) [pdf, other]
Title: Quantum coarse-grained entropy and thermodynamics
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
[33]  arXiv:1709.04925 (replaced) [pdf, other]
Title: Interpretation of quantum mechanics with indefinite norm
Comments: 18 pages, 3 figures. v2: added discussion about oscillations into sterile neutrinos with negative norm and MiniBoone anomaly; extra references
Subjects: Quantum Physics (quant-ph); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
[34]  arXiv:1709.06615 (replaced) [pdf, other]
Title: Permutational symmetries for coincidence rates in multi-mode multi-photonic interferometry
Journal-ref: Phys. Rev. A 97, 063802 (2018)
Subjects: Quantum Physics (quant-ph); Optics (physics.optics)
[35]  arXiv:1710.07629 (replaced) [pdf, other]
Title: OpenFermion: The Electronic Structure Package for Quantum Computers
Subjects: Quantum Physics (quant-ph); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
[36]  arXiv:1711.09132 (replaced) [pdf, other]
Title: Multiparameter Gaussian Quantum Metrology
Comments: 14 pages, 3 figures; expanded and updated; to appear in Physical Review A
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Instrumentation and Detectors (physics.ins-det); Optics (physics.optics)
[37]  arXiv:1803.02561 (replaced) [pdf, other]
Title: Theory of 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)
[38]  arXiv:1803.04747 (replaced) [pdf, other]
Title: Quasiprobability representation of quantum coherence
Journal-ref: Phys. Rev. A 97, 062327 (2018)
Subjects: Quantum Physics (quant-ph)
[39]  arXiv:1804.04506 (replaced) [pdf, other]
Title: Few-fermion thermometry
Journal-ref: Phys. Rev. A 97, 063619 (2018)
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
[40]  arXiv:1804.05987 (replaced) [pdf, other]
Title: Direct computation of the quantum partition function by path-integral nested sampling
Subjects: Quantum Physics (quant-ph); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph)
[41]  arXiv:1805.08823 (replaced) [pdf, other]
Title: Pulsed excitation dynamics in quantum dot-cavity systems: limits to optimizing the fidelity of on-demand single photon sources
Subjects: Quantum Physics (quant-ph)
[42]  arXiv:1806.02359 (replaced) [pdf, other]
Title: Fault tolerance in the IBM Q Experience
Comments: Clarified fitting assumptions. 4+2 pages, 3 figures
Subjects: Quantum Physics (quant-ph)
[43]  arXiv:1806.04281 (replaced) [pdf, other]
Title: Chaos signatures in the short and long time behavior of the out-of-time ordered correlator
Comments: 4+1/2 pages + small appendix -- Small changes, and many typos corrected
Subjects: Quantum Physics (quant-ph); Chaotic Dynamics (nlin.CD)
[44]  arXiv:1806.05150 (replaced) [pdf, other]
Title: Phase-locking between different partial-waves in atom-ion spin-exchange collisions
Comments: 5 pages, 5 figures and Supplemental Material
Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
[45]  arXiv:1806.05166 (replaced) [pdf, other]
Title: Reference-frame-independent measurement-device-independent quantum key distribution based on polarization multiplexing