## Journals

### Generalized Probabilistic Description of Noninteracting Identical Particles

Author(s): Marcin Karczewski, Marcin Markiewicz, Dagomir Kaszlikowski, and Paweł Kurzyński

We investigate an operational description of identical noninteracting particles in multiports. In particular, we look for physically motivated restrictions that explain their bunching probabilities. We focus on a symmetric 3-port in which a triple of superquantum particles admitted by our generalize...

[Phys. Rev. Lett. 120, 080401] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Atypicality of Most Few-Body Observables

Author(s): Ryusuke Hamazaki and Masahito Ueda

The eigenstate thermalization hypothesis (ETH), which dictates that all diagonal matrix elements within a small energy shell be almost equal, is a major candidate to explain thermalization in isolated quantum systems. According to the typicality argument, the maximum variations of such matrix elemen...

[Phys. Rev. Lett. 120, 080603] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Achieving a strongly negative scattering asymmetry factor in random media composed of dual-dipolar particles

Author(s): B. X. Wang and C. Y. Zhao

Understanding radiative transfer in random media like micro- or nanoporous and particulate materials, allows people to manipulate the scattering and absorption of radiation, as well as opens new possibilities in applications such as imaging through turbid media, photovoltaics, and radiative cooling....

[Phys. Rev. A 97, 023836] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Analytical modeling of parametrically modulated transmon qubits

PRA: Quantum information - Fri, 2018-02-23 11:00

Author(s): Nicolas Didier, Eyob A. Sete, Marcus P. da Silva, and Chad Rigetti

Building a scalable quantum computer requires developing appropriate models to understand and verify its complex quantum dynamics. We focus on superconducting quantum processors based on transmons for which full numerical simulations are already challenging at the level of qubytes. It is thus highly...

[Phys. Rev. A 97, 022330] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Entanglement increase from local interaction in the absence of initial quantum correlation in the environment and between the system and the environment

PRA: Quantum information - Fri, 2018-02-23 11:00

Author(s): Iman Sargolzahi and Sayyed Yahya Mirafzali

We consider a bipartite quantum system S=AB such that the part A is isolated from the environment E and only the part B interacts with E. Under such circumstances, entanglement of the system may experience decreases and increases, during the evolution of the system. Here, we show that the entangleme...

[Phys. Rev. A 97, 022331] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Efficient quantum pseudorandomness with simple graph states

PRA: Quantum information - Fri, 2018-02-23 11:00

Author(s): Rawad Mezher, Joe Ghalbouni, Joseph Dgheim, and Damian Markham

Measurement based (MB) quantum computation allows for universal quantum computing by measuring individual qubits prepared in entangled multipartite states, known as graph states. Unless corrected for, the randomness of the measurements leads to the generation of ensembles of random unitaries, where ...

[Phys. Rev. A 97, 022333] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Local distinguishability of orthogonal quantum states with multiple copies of $2⊗2$ maximally entangled states

PRA: Quantum information - Fri, 2018-02-23 11:00

Author(s): Zhi-Chao Zhang, Yan-Qi Song, Ting-Ting Song, Fei Gao, Su-Juan Qin, and Qiao-Yan Wen

For general quantum systems, many sets of locally indistinguishable orthogonal quantum states have been constructed so far. However, it is interesting how much entanglement resources are sufficient and/or necessary to distinguish these states by local operations and classical communication (LOCC). H...

[Phys. Rev. A 97, 022334] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Implementing universal nonadiabatic holonomic quantum gates with transmons

PRA: Quantum information - Fri, 2018-02-23 11:00

Author(s): Zhuo-Ping Hong, Bao-Jie Liu, Jia-Qi Cai, Xin-Ding Zhang, Yong Hu, Z. D. Wang, and Zheng-Yuan Xue

Geometric phases are well known to be noise resilient in quantum evolutions and operations. Holonomic quantum gates provide us with a robust way towards universal quantum computation, as these quantum gates are actually induced by non-Abelian geometric phases. Here we propose and elaborate how to ef...

[Phys. Rev. A 97, 022332] Published Fri Feb 23, 2018

Categories: Journals, Physics

### Facilitated quantum cellular automata as simple models with nonthermal eigenstates and dynamics. (arXiv:1802.07729v1 [cond-mat.stat-mech])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We introduce and describe a class of simple facilitated quantum spin models in which the dynamics is due to the repeated application of unitary gates. The gates are applied periodically in time, so their combined action constitutes a Floquet unitary. The dynamics of the models we discuss can be classically simulated, and their eigenstates classically constructed (although they are highly entangled). We consider a variety of models in both one and two dimensions, involving Clifford gates and Toffoli gates. For some of these models, we explicitly construct conserved densities; thus these models are "integrable." The other models do not seem to be integrable; yet, for some system sizes and boundary conditions, their eigenstate entanglement is strongly subthermal. Some of the models have exponentially many eigenstates in which one or more sites are "disentangled" from the rest of the system, as a consequence of reflection symmetry.

Categories: Journals, Physics

### Contextuality bounds the efficiency of classical simulation of quantum processes. (arXiv:1802.07744v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

Contextuality has been conjectured to be a super-classical resource for quantum computation, analogous to the role of non-locality as a super-classical resource for communication. We show that the presence of contextuality places a lower bound on the amount of classical memory required to simulate any quantum sub-theory, thereby establishing a quantitative connection between contextuality and classical simulability. We apply our result to the qubit stabilizer sub-theory, where the presence of state-independent contextuality has been an obstacle in establishing contextuality as a quantum computational resource. We find that the presence of contextuality in this sub-theory demands that the minimum number of classical bits of memory required to simulate a multi-qubit system must scale quadratically in the number of qubits; notably, this is the same scaling as the Gottesman-Knill algorithm. We contrast this result with the (non-contextual) qudit case, where linear scaling is possible.

Categories: Journals, Physics

### Communication Complexity of One-Shot Remote State Preparation. (arXiv:1802.07795v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

Quantum teleportation uses prior shared entanglement and classical communication to send an unknown quantum state from one party to another. Remote state preparation (RSP) is a similar distributed task in which the sender knows the entire classical description of the state to be sent. (This may also be viewed as the task of non-oblivious compression of a single sample from an ensemble of quantum states.) We study the communication complexity of approximate remote state preparation, in which the goal is to prepare an approximation of the desired quantum state. Jain [Quant. Inf. & Comp., 2006] showed that the worst-case communication complexity of approximate RSP can be bounded from above in terms of the maximum possible information in an encoding. He also showed that this quantity is a lower bound for communication complexity of (exact) remote state preparation. In this work, we tightly characterize the worst-case and average-case communication complexity of remote state preparation in terms of non-asymptotic information-theoretic quantities. We also show that the average-case communication complexity of RSP can be much smaller than the worst-case one. In the process, we show that n bits cannot be communicated with less than n transmitted bits in LOCC protocols. This strengthens a result due to Nayak and Salzman [J. ACM, 2006] and may be of independent interest.

Categories: Journals, Physics

### A conditionally integrable Schr\"odinger potential of a bi-confluent Heun class. (arXiv:1802.07821v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We present a bi-confluent Heun potential for the Schr\"odinger equation involving inverse fractional powers and a repulsive centrifugal-barrier term the strength of which is fixed to a constant. This is an infinite potential well defined on the positive half-axis. Each of the fundamental solutions for this conditionally integrable potential is written as an irreducible linear combination of two Hermite functions of a shifted and scaled argument. We present the general solution of the problem, derive the exact energy spectrum equation and construct a highly accurate approximation for the bound-state energy levels.

Categories: Journals, Physics

### Quantum Divide-and-Conquer Anchoring for Separable Non-negative Matrix Factorization. (arXiv:1802.07828v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

It is NP-complete to find non-negative factors $W$ and $H$ with fixed rank $r$ from a non-negative matrix $X$ by minimizing $\|X-WH^\top\|_F^2$. Although the separability assumption (all data points are in the conical hull of the extreme rows) enables polynomial-time algorithms, the computational cost is not affordable for big data. This paper investigates how the power of quantum computation can be capitalized to solve the non-negative matrix factorization with the separability assumption (SNMF) by devising a quantum algorithm based on the divide-and-conquer anchoring (DCA) scheme. The design of quantum DCA (QDCA) is challenging. In the divide step, the random projections in DCA is completed by a quantum algorithm for linear operations, which achieves the exponential speedup. We then devise a heuristic post-selection procedure which extracts the information of anchors stored in the quantum states efficiently. Under a plausible assumption, QDCA performs efficiently, achieves the quantum speedup, and is beneficial for high dimensional problems.

Categories: Journals, Physics

### Tutorial: Magnetic resonance with nitrogen-vacancy centers in diamond---microwave engineering, materials science, and magnetometry. (arXiv:1802.07857v1 [cond-mat.mtrl-sci])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

This tutorial article provides a concise and pedagogical overview on negatively-charged nitrogen-vacancy (NV) centers in diamond. The research on the NV centers has attracted enormous attention for its application to quantum sensing, encompassing the areas of not only physics and applied physics but also chemistry, biology and life sciences. Nonetheless, its key technical aspects can be understood from the viewpoint of magnetic resonance. We focus on three facets of this ever-expanding research field, to which our viewpoint is especially relevant: microwave engineering, materials science, and magnetometry. In explaining these aspects, we provide a technical basis and up-to-date technologies for the research on the NV centers.

Categories: Journals, Physics

### Interlayer Couplings Mediated by Antiferromagnetic Magnons. (arXiv:1802.07867v1 [cond-mat.mes-hall])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

Collinear antiferromagnets (AFs) support two degenerate magnon excitations carrying opposite spin polarizations, by which magnons can function as electrons in spin transport. We explore the interlayer coupling mediated by antiferromagnetic magnons in an insulating ferromagnet (F)/AF/F trilayer structure. The internal energy of the AF depends on the orientations of the two Fs, which manifests as effective interlayer interactions JS1.S2 and K(S1.S2)^2. Both J and K are functions of temperature and the AF thickness. Interestingly, J is antiferromagnetic at low temperatures and ferromagnetic at high temperatures. In the high-temperature regime, J is estimated to be much larger than the interlayer dipole-dipole interaction, allowing direct experimental verification.

Categories: Journals, Physics

### Would quantum entanglement be increased by anti-Unruh effect?. (arXiv:1802.07886v1 [gr-qc])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We study the "anti-Unruh effect" for an entangled quantum state in reference to the counterintuitive cooling previously pointed out for an accelerated detector coupled to the vacuum. We show that quantum entanglement for an initially entangled (spacelike separated) bipartite state can be increased when either a detector attached to one particle is accelerated or both detectors attached to the two particles are in simultaneous accelerations. However, if the two particles (e.g., detectors for the bipartite system) are not initially entangled, entanglement cannot be created by the anti-Unruh effect. Thus, within certain parameter regime, this work shows that the anti-Unruh effect can be viewed as an amplification mechanism for quantum entanglement.

Categories: Journals, Physics

### Improving sensitivity to magnetic fields and electric dipole moments by using measurements of individual magnetic sublevels. (arXiv:1802.07892v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We explore ways to use the ability to measure the populations of individual magnetic sublevels to improve the sensitivity of magnetic field measurements and measurements of atomic electric dipole moments (EDMs). When atoms are initialized in the $m=0$ magnetic sublevel, the shot-noise-limited uncertainty of these measurements is $1/\sqrt{2F(F+1)}$ smaller than that of a Larmor precession measurement. When the populations in the even (or odd) magnetic sublevels are combined, we show that these measurements are independent of the tensor Stark shift and the second order Zeeman shift. We discuss the complicating effect of a transverse magnetic field and show that when the ratio of the tensor Stark shift to the transverse magnetic field is sufficiently large, an EDM measurement with atoms initialized in the superposition of the stretched states can reach the optimal sensitivity.

Categories: Journals, Physics

### Longer distance continuous variable quantum key distribution protocol with photon subtraction at receiver. (arXiv:1802.07915v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

One of the limitation of continuous variable quantum key distribution is relatively short transmission distance of secure keys. In order to overcome the limitation, some solutions have been proposed such as reverse reconciliation, trusted noise concept, and non-Gaussian operation. In this paper, we propose a protocol using photon subtraction at receiver which utilizes synergy of the aforementioned properties. By simulations, we show performance of the proposed protocol outperforms other conventional protocols. We also find the protocol is more efficient in a practical case. Finally, we provide a guide for provisioning a system based on the protocol through an analysis for noise from a channel.

Categories: Journals, Physics

### Symmetric Tops Subject to Combined Electric Fields: Conditional Quasi-Solvability via the Quantum Hamilton-Jacobi Theory. (arXiv:1802.07939v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We make use of the Quantum Hamilton-Jacobi (QHJ) theory to investigate conditional quasi-solvability of the quantum symmetric top subject to combined electric fields (symmetric top pendulum). We derive the conditions of quasi-solvability of the time-independent Schroedinger equation as well as the corresponding finite sets of exact analytic solutions. We do so for this prototypical trigonometric system as well as for its anti-isospectral hyperbolic counterpart. An examination of the algebraic and numerical spectra of these two systems reveals mutually closely related patterns. The QHJ approach allows to retrieve the closed-form solutions for the spherical and planar pendula and the Razavy system that had been obtained in our earlier work via Supersymmetric Quantum Mechanics as well as to find a cornucopia of additional exact analytic solutions.

Categories: Journals, Physics

### A two-way quantum interface for linking $\text{Sr}^{\text{+}}$ transition at 422nm to the telecommunications C-band. (arXiv:1802.07947v1 [quant-ph])

arXiv.org: Quantum Physics - Fri, 2018-02-23 02:45

We report a single-stage bi-directional interface capable of linking Sr$^+$ trapped ion qubits in a long-distance quantum network. Our interface converts photons between the Sr$^+$ emission wavelength at 422 nm and the telecoms C-band to enable low-loss transmission over optical fiber. We have achieved both up- and down-conversion at the single photon level with efficiencies of 9.4 $\%$ and 1.1 $\%$ respectively. Furthermore, we demonstrate that the noise introduced during the conversion process is sufficiently low to implement high-fidelity interconnects suitable for quantum networking.

Categories: Journals, Physics