Quantum

Halving the cost of quantum addition

Craig Gidney,

Quantum 2, 74 (2018). https://doi.org/10.22331/q-2018-06-18-74

We improve the number of T gates needed to perform an n-bit adder from $8n + O(1)$ to $4n + O(1)$. We do so via a "temporary logical-AND" construction which uses four T gates to store the lo…

Paper

Heralded generation of maximal entanglement in any dimension via incoherent coupling to thermal baths

Armin Tavakoli, Géraldine Haack, Marcus Huber, Nicolas Brunner, and Jonatan Bohr Brask,

Quantum 2, 73 (2018). https://doi.org/10.22331/q-2018-06-13-73

We present a scheme for dissipatively generating maximal entanglement in a heralded manner. Our setup requires incoherent interactions with two thermal baths at different temperatures, but n…

Paper

Robust Bell inequalities from communication complexity

Sophie Laplante, Mathieu Laurière, Alexandre Nolin, Jérémie Roland, and Gabriel Senno,

Quantum 2, 72 (2018). https://doi.org/10.22331/q-2018-06-07-72

The question of how large Bell inequality violations can be, for quantum distributions, has been the object of much work in the past several years. We say that a Bell inequality is normalize…

Paper

Codes and Protocols for Distilling $T$, controlled-$S$, and Toffoli Gates

Jeongwan Haah and Matthew B. Hastings,

Quantum 2, 71 (2018). https://doi.org/10.22331/q-2018-06-07-71

We present several different codes and protocols to distill $T$, controlled-$S$, and Toffoli (or $CCZ$) gates. One construction is based on codes that generalize the triorthogonal codes, all…

Paper

Phonon-assisted relaxation and decoherence of singlet-triplet qubits in Si/SiGe quantum dots

Viktoriia Kornich, Christoph Kloeffel, and Daniel Loss,

Quantum 2, 70 (2018). https://doi.org/10.22331/q-2018-05-28-70

We study theoretically the phonon-induced relaxation and decoherence of spin states of two electrons in a lateral double quantum dot in a SiGe/Si/SiGe heterostructure. We consider two types…

Paper

Scattering into one-dimensional waveguides from a coherently-driven quantum-optical system

Kevin A. Fischer, Rahul Trivedi, Vinay Ramasesh, Irfan Siddiqi, and Jelena Vučković,

Quantum 2, 69 (2018). https://doi.org/10.22331/q-2018-05-28-69

We develop a new computational tool and framework for characterizing the scattering of photons by energy-nonconserving Hamiltonians into unidirectional (chiral) waveguides, for example, with…

Paper

Scalable Neural Network Decoders for Higher Dimensional Quantum Codes

Nikolas P. Breuckmann and Xiaotong Ni,

Quantum 2, 68 (2018). https://doi.org/10.22331/q-2018-05-24-68

Machine learning has the potential to become an important tool in quantum error correction as it allows the decoder to adapt to the error distribution of a quantum chip. An additional motiva…

Paper

Coarse-grained distinguishability of field interactions

Cédric Bény,

Quantum 2, 67 (2018). https://doi.org/10.22331/q-2018-05-24-67

Information-theoretical quantities such as statistical distinguishability typically result from optimisations over all conceivable observables. Physical theories, however, are not generally…

Paper

Fluctuation-dissipation theorem for non-equilibrium quantum systems

Mohammad Mehboudi, Anna Sanpera, and Juan M. R. Parrondo,

Quantum 2, 66 (2018). https://doi.org/10.22331/q-2018-05-24-66

The fluctuation-dissipation theorem (FDT) is a central result in statistical physics, both for classical and quantum systems. It establishes a relationship between the linear response of a s…

Paper

Anticoncentration theorems for schemes showing a quantum speedup

Dominik Hangleiter, Juan Bermejo-Vega, Martin Schwarz, and Jens Eisert,

Quantum 2, 65 (2018). https://doi.org/10.22331/q-2018-05-22-65

One of the main milestones in quantum information science is to realise quantum devices that exhibit an exponential computational advantage over classical ones without being universal quantu…

Paper

Distribution of entanglement and correlations in all finite dimensions

Christopher Eltschka and Jens Siewert,

Quantum 2, 64 (2018). https://doi.org/10.22331/q-2018-05-22-64

The physics of a many-particle system is determined by the correlations in its quantum state. Therefore, analyzing these correlations is the foremost task of many-body physics. Any 'a priori…

Paper

Causation does not explain contextuality

Sally Shrapnel and Fabio Costa,

Quantum 2, 63 (2018). https://doi.org/10.22331/q-2018-05-18-63

Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-…

Paper

Lattice Surgery with a Twist: Simplifying Clifford Gates of Surface Codes

Daniel Litinski and Felix von Oppen,

Quantum 2, 62 (2018). https://doi.org/10.22331/q-2018-05-04-62

We present a planar surface-code-based scheme for fault-tolerant quantum computation which eliminates the time overhead of single-qubit Clifford gates, and implements long-range multi-target…

Paper

Precision and Work Fluctuations in Gaussian Battery Charging

Nicolai Friis and Marcus Huber,

Quantum 2, 61 (2018). https://doi.org/10.22331/q-2018-04-23-61

One of the most fundamental tasks in quantum thermodynamics is extracting energy from one system and subsequently storing this energy in an appropriate battery. Both of these steps, work ext…

Paper

Gauge invariant information concerning quantum channels

Łukasz Rudnicki, Zbigniew Puchała, and Karol Zyczkowski,

Quantum 2, 60 (2018). https://doi.org/10.22331/q-2018-04-11-60

Motivated by the gate set tomography we study quantum channels from the perspective of information which is invariant with respect to the gauge realized through similarity of matrices repres…

Paper

Additivity of entropic uncertainty relations

René Schwonnek,

Quantum 2, 59 (2018). https://doi.org/10.22331/q-2018-03-30-59

We consider the uncertainty between two pairs of local projective measurements performed on a multipartite system. We show that the optimal bound in any linear uncertainty relation, formulat…

Paper

Dissipative stabilization of entangled cat states using a driven Bose-Hubbard dimer

M. Mamaev, L. C. G. Govia, and A. A. Clerk,

Quantum 2, 58 (2018). https://doi.org/10.22331/q-2018-03-27-58

We analyze a modified Bose-Hubbard model, where two cavities having on-site Kerr interactions are subject to two-photon driving and correlated dissipation. We derive an exact solution for th…

Paper

Non-Shannon inequalities in the entropy vector approach to causal structures

Mirjam Weilenmann and Roger Colbeck,

Quantum 2, 57 (2018). https://doi.org/10.22331/q-2018-03-14-57

A causal structure is a relationship between observed variables that in general restricts the possible correlations between them. This relationship can be mediated by unobserved systems, mod…

Paper

Magic state parity-checker with pre-distilled components

Earl T. Campbell and Mark Howard,

Quantum 2, 56 (2018). https://doi.org/10.22331/q-2018-03-14-56

Magic states are eigenstates of non-Pauli operators. One way of suppressing errors present in magic states is to perform parity measurements in their non-Pauli eigenbasis and postselect on e…

Paper

Sandwiched Rényi Convergence for Quantum Evolutions

Alexander Müller-Hermes and Daniel Stilck Franca,

Quantum 2, 55 (2018). https://doi.org/10.22331/q-2018-02-27-55

We study the speed of convergence of a primitive quantum time evolution towards its fixed point in the distance of sandwiched Rényi divergences. For each of these distance measures the conve…

Paper

Quantum Horn’s lemma, finite heat baths, and the third law of thermodynamics

Jakob Scharlau and Markus P. Mueller,

Quantum 2, 54 (2018). https://doi.org/10.22331/q-2018-02-22-54

Interactions of quantum systems with their environment play a crucial role in resource-theoretic approaches to thermodynamics in the microscopic regime. Here, we analyze the possible state t…

Paper

Flag fault-tolerant error correction with arbitrary distance codes

Christopher Chamberland and Michael E. Beverland,

Quantum 2, 53 (2018). https://doi.org/10.22331/q-2018-02-08-53

In this paper we introduce a general fault-tolerant quantum error correction protocol using flag circuits for measuring stabilizers of arbitrary distance codes. In addition to extending flag…

Paper

Elementary Thermal Operations

Matteo Lostaglio, Álvaro M. Alhambra, and Christopher Perry,

Quantum 2, 52 (2018). https://doi.org/10.22331/q-2018-02-08-52

To what extent do thermodynamic resource theories capture physically relevant constraints? Inspired by quantum computation, we define a set of elementary thermodynamic gates that only act on…

Paper

Characterization of linear maps on $M_n$ whose multiplicity maps have maximal norm, with an application in quantum information

Daniel Puzzuoli,

Quantum 2, 51 (2018). https://doi.org/10.22331/q-2018-02-05-51

Given a linear map $\Phi : M_n \rightarrow M_m$, its multiplicity maps are defined as the family of linear maps $\Phi \otimes \textrm{id}_{k} : M_n \otimes M_k \rightarrow M_m \otimes M_k$,…

Paper

Bond dimension witnesses and the structure of homogeneous matrix product states

Miguel Navascues and Tamas Vertesi,

Quantum 2, 50 (2018). https://doi.org/10.22331/q-2018-01-31-50

For the past twenty years, Matrix Product States (MPS) have been widely used in solid state physics to approximate the ground state of one-dimensional spin chains. In this paper, we study ho…

Paper

ProjectQ: an open source software framework for quantum computing

Damian S. Steiger, Thomas Häner, and Matthias Troyer,

Quantum 2, 49 (2018). https://doi.org/10.22331/q-2018-01-31-49

We introduce ProjectQ, an open source software effort for quantum computing. The first release features a compiler framework capable of targeting various types of hardware, a high-performanc…

Paper

Machine-learning-assisted correction of correlated qubit errors in a topological code

Paul Baireuther, Thomas E. O’Brien, Brian Tarasinski, and Carlo W. J. Beenakker,

Quantum 2, 48 (2018). https://doi.org/10.22331/q-2018-01-29-48

A fault-tolerant quantum computation requires an efficient means to detect and correct errors that accumulate in encoded quantum information. In the context of machine learning, neural netwo…

Paper

Randomized benchmarking with gate-dependent noise

Joel J. Wallman,

Quantum 2, 47 (2018). https://doi.org/10.22331/q-2018-01-29-47

We analyze randomized benchmarking for arbitrary gate-dependent noise and prove that the exact impact of gate-dependent noise can be described by a single perturbation term that decays expon…

Paper

Vacuum source-field correlations and advanced waves in quantum optics

Adam Stokes,

Quantum 2, 46 (2018). https://doi.org/10.22331/q-2018-01-18-46

The solution to the wave equation as a Cauchy problem with prescribed fields at an initial time $t=0$ is purely retarded. Similarly, in the quantum theory of radiation the specification of H…

Paper

Separability of diagonal symmetric states: a quadratic conic optimization problem

Jordi Tura, Albert Aloy, Ruben Quesada, Maciej Lewenstein, and Anna Sanpera,

Quantum 2, 45 (2018). https://doi.org/10.22331/q-2018-01-12-45

We study the separability problem in mixtures of Dicke states i.e., the separability of the so-called Diagonal Symmetric (DS) states. First, we show that separability in the case of DS in $C^d\otimes C^d$…

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