Author(s): Daniel C. Murphy and Kenneth R. Brown

The success probability of a quantum algorithm constructed from noisy quantum gates cannot be accurately predicted from single-parameter metrics that compare noisy and ideal gates. We illustrate this concept by examining a system with coherent errors and comparing algorithm success rates for differe...

[Phys. Rev. A 99, 032318] Published Thu Mar 14, 2019

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Author(s): Andrés Vallejo, Alejandro Romanelli, Raúl Donangelo, and Renato Portugal

We explore the notion of generated entropy in open quantum systems. We focus on the study of the discrete-time quantum walk on the line, from the entropy production perspective. We argue that the evolution of the coin can be modeled as an open two-level system that exchanges energy with the lattice ...

[Phys. Rev. A 99, 032319] Published Thu Mar 14, 2019

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Author(s): Gautam Kamalakar Naik, Rajeev Singh, and Sunil Kumar Mishra

We propose a method for generation of genuine multipartite entangled states in a short-range Ising spin chain with periodic global pulses of magnetic field. We consider an integrable and a nonintegrable Floquet system that is periodic in time and has constant quasienergy gaps with degeneracies. We s...

[Phys. Rev. A 99, 032321] Published Thu Mar 14, 2019

Author(s): Alexandre C. Orthey, Jr. and Edgard P. M. Amorim

We investigate the relation between transport properties and entanglement between the internal (spin) and external (position) degrees of freedom in one-dimensional discrete time quantum walks. We obtain closed-form expressions for the long-time position variance and asymptotic entanglement of quantu...

[Phys. Rev. A 99, 032320] Published Thu Mar 14, 2019

- Read more about Connecting velocity and entanglement in quantum walks
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Molecular electronics is a rapidly developing field focused on using

molecules as the structural basis for electronic components. It is common in

such devices for the system of interest to couple simultaneously to multiple

environments. Here we consider a model comprised of a double quantum dot (or

molecule) coupled strongly to vibrations and weakly to two electronic leads

held at arbitrary bias voltage. The strong vibrational coupling invalidates

treating the bosonic and electronic environments simply as acting additively,

We report a high-resolution terahertz spectroscopic study of quantum spin

dynamics in the antiferromagnetic Heisenberg-Ising spin-chain compound

BaCo$_2$V$_2$O$_8$ as a function of temperature and longitudinal magnetic

field. Confined spinon excitations are observed in an antiferromagnetic phase

below $T_N\simeq 5.5$ K. In a field-induced gapless phase above $B_c=3.8$ T, we

identify many-body string excitations as well as low-energy fractional

psinon/antipsinon excitations by comparing to Bethe-Ansatz calculations. In the

In this work we present an effective Hamiltonian description of the quantum

dynamics of a generalized Lambda system undergoing adiabatic evolution. We

assume the system to be initialized in the dark subspace and show that its

holonomic evolution can be viewed as a conventional Hamiltonian dynamics in an

appropriately chosen extended Hilbert space. In contrast to the existing

approaches, our method does not require the calculation of the non-Abelian

Berry connection and can be applied without any parametrization of the dark

We define a property called nondegeneracy for Bell inequalities, which

describes the situation that in a Bell setting, if a Bell inequality and

involved local measurements are chosen and fixed, any quantum state with a

given dimension and its orthogonal quantum state cannot violate the inequality

remarkably at the same time. We prove that for an arbitrary quantum dimension,

based on the measurement statistics only, we can give an analytic lower bound

for the entanglement of formation of the unknown bipartite quantum state by

The creation of matter and structure in our universe is currently described

by an intricate interplay of quantum field theory and general relativity.

Signatures of this process during an early inflationary period can be observed,

while direct tests remain out of reach. Here, we study an experimental analog

of the process based on trapped atomic ions. We create pairs of phonons by

tearing apart quantum vacuum fluctuations. Thereby, we prepare ions in an

entangled state of motion. Controlling timescales and the coupling to

We investigate the emergence of temperature $T$ in the system-plus-reservoir

paradigm starting from the fundamental microcanonical scenario at total fixed

energy $E$ where, contrary to the canonical approach, $T=T(E)$ is not a control

parameter but a derived auxiliary concept. As shown by Schwinger for the regime

of weak coupling $\gamma$ between system and environment, $T(E)$ emerges from

the saddle-point analysis leading to the ensemble equivalence up to corrections