Quantum

Paper

An initialization strategy for addressing barren plateaus in parametrized quantum circuits

Edward Grant, Leonard Wossnig, Mateusz Ostaszewski, and Marcello Benedetti,

Quantum 3, 214 (2019).

Parametrized quantum circuits initialized with random initial parameter values are characterized by barren plateaus where the gradient becomes exponentially small in the number of qubits. In…

Paper

Exact Markovian and non-Markovian time dynamics in waveguide QED: collective interactions, bound states in continuum, superradiance and subradiance

Fatih Dinc, İlke Ercan, and Agata M. Brańczyk,

Quantum 3, 213 (2019).

We develop a formalism for modelling $exact$ time dynamics in waveguide quantum electrodynamics (QED) using the real-space approach. The formalism does not assume any specific configuration…

Paper

A Silicon Surface Code Architecture Resilient Against Leakage Errors

Zhenyu Cai, Michael A. Fogarty, Simon Schaal, Sofia Patomäki, Simon C. Benjamin, and John J. L. Morton,

Quantum 3, 212 (2019).

Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing sem…

Paper

Exploring the limits of no backwards in time signalling

Yelena Guryanova, Ralph Silva, Anthony J. Short, Paul Skrzypczyk, Nicolas Brunner, and Sandu Popescu,

Quantum 3, 211 (2019).

We present an operational and model-independent framework to investigate the concept of no-backwards-in-time signalling. We define no-backwards-in-time signalling conditions, closely related…

Paper

Graded-index optical fiber emulator of an interacting three-atom system: illumination control of particle statistics and classical non-separability

M.A. Garcia-March, N.L. Harshman, H. da Silva, T. Fogarty, Th. Busch, M. Lewenstein, and A. Ferrando,

Quantum 3, 210 (2019).

We show that a system of three trapped ultracold and strongly interacting atoms in one-dimension can be emulated using an optical fiber with a graded-index profile and thin metallic slabs. W…

Paper

An information-theoretic treatment of quantum dichotomies

Francesco Buscemi, David Sutter, and Marco Tomamichel,

Quantum 3, 209 (2019).

Given two pairs of quantum states, we want to decide if there exists a quantum channel that transforms one pair into the other. The theory of quantum statistical comparison and quantum relat…

Paper

Qubitization of Arbitrary Basis Quantum Chemistry Leveraging Sparsity and Low Rank Factorization

Dominic W. Berry, Craig Gidney, Mario Motta, Jarrod R. McClean, and Ryan Babbush,

Quantum 3, 208 (2019).

Recent work has dramatically reduced the gate complexity required to quantum simulate chemistry by using linear combinations of unitaries based methods to exploit structure in the plane wave…

Paper

Ergodicity probes: using time-fluctuations to measure the Hilbert space dimension

Charlie Nation and Diego Porras,

Quantum 3, 207 (2019).

Quantum devices, such as quantum simulators, quantum annealers, and quantum computers, may be exploited to solve problems beyond what is tractable with classical computers. This may be achie…

Paper

Time-delocalized quantum subsystems and operations: on the existence of processes with indefinite causal structure in quantum mechanics

Ognyan Oreshkov,

Quantum 3, 206 (2019).

It has been shown that it is theoretically possible for there to exist higher-order quantum processes in which the operations performed by separate parties cannot be ascribed a definite caus…

Paper

Magic State Distillation: Not as Costly as You Think

Daniel Litinski,

Quantum 3, 205 (2019).

Despite significant overhead reductions since its first proposal, magic state distillation is often considered to be a very costly procedure that dominates the resource cost of fault-toleran…

Paper

k-stretchability of entanglement, and the duality of k-separability and k-producibility

Szilárd Szalay,

Quantum 3, 204 (2019).

The notions of $k$-separability and $k$-producibility are useful and expressive tools for the characterization of entanglement in multipartite quantum systems, when a more detailed analysis…

Paper

Separability for mixed states with operator Schmidt rank two

Gemma De las Cuevas, Tom Drescher, and Tim Netzer,

Quantum 3, 203 (2019).

The operator Schmidt rank is the minimum number of terms required to express a state as a sum of elementary tensor factors. Here we provide a new proof of the fact that any bipartite mixed s…

Paper

Decomposable coherence and quantum fluctuation relations

Erick Hinds Mingo and David Jennings,

Quantum 3, 202 (2019).

In Newtonian mechanics, any closed-system dynamics of a composite system in a microstate will leave all its individual subsystems in distinct microstates, however this fails dramatically in…

Paper

Duality in Quantum Quenches and Classical Approximation Algorithms: Pretty Good or Very Bad

Matthew B. Hastings,

Quantum 3, 201 (2019).

We consider classical and quantum algorithms which have a duality property: roughly, either the algorithm provides some nontrivial improvement over random or there exist many solutions which…

Paper

Phase diffusion and the small-noise approximation in linear amplifiers: Limitations and beyond

Andy Chia, Michal Hajdušek, Rosario Fazio, Leong-Chuan Kwek, and Vlatko Vedral,

Quantum 3, 200 (2019).

The phase of an optical field inside a linear amplifier is widely known to diffuse with a diffusion coefficient that is inversely proportional to the photon number. The same process occurs i…

Paper

Tensorization of the strong data processing inequality for quantum chi-square divergences

Yu Cao and Jianfeng Lu,

Quantum 3, 199 (2019).

It is well-known that any quantum channel $\mathcal{E}$ satisfies the data processing inequality (DPI), with respect to various divergences, e.g., quantum $\chi^2_{\kappa}$ divergences and q…

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