Archives: Paper

Christopher Chamberland, Pavithran Iyer, and David Poulin,

Quantum 2, 43 (2018). https://doi.org/10.22331/q-2018-01-04-43

We consider the problem of fault-tolerant quantum computation in the presence of slow error diagnostics, either caused by measurement latencies or slow decoding algorithms. Our scheme offers…

Louis Villa and Gabriele De Chiara,

Quantum 2, 42 (2018). https://doi.org/10.22331/q-2018-01-04-42

We propose a method to experimentally measure the internal energy of a system of ultracold atoms trapped in optical lattices by coupling them to the fields of two optical cavities. We show t…

Eduardo Mascarenhas, Giacomo Giudice, and Vincenzo Savona,

Quantum 1, 40 (2017). https://doi.org/10.22331/q-2017-12-20-40

We study spin transport in a boundary driven XXZ spin chain. Driving at the chain boundaries is modeled by two additional spin chains prepared in oppositely polarized states. Emergent behavi…

Alastair A. Abbott, Julian Wechs, Fabio Costa, and Cyril Branciard,

Quantum 1, 39 (2017). https://doi.org/10.22331/q-2017-12-14-39

The study of correlations with no definite causal order has revealed a rich structure emerging when more than two parties are involved. This motivates the consideration of multipartite "nonc…

Philipp Andres Höhn,

Quantum 1, 38 (2017). https://doi.org/10.22331/q-2017-12-14-38

We develop an operational approach for reconstructing the quantum theory of qubit systems from elementary rules on information acquisition. The focus lies on an observer $O$ interrogating a…

Stefan Nimmrichter, Jibo Dai, Alexandre Roulet, and Valerio Scarani,

Quantum 1, 37 (2017). https://doi.org/10.22331/q-2017-12-11-37

We study the quantum and classical evolution of a system of three harmonic modes interacting via a trilinear Hamiltonian. With the modes prepared in thermal states of different temperatures,…

Leonardo Banchi, Enrico Compagno, Vladimir Korepin, and Sougato Bose,

Quantum 1, 36 (2017). https://doi.org/10.22331/q-2017-11-30-36

We show how the spin independent scattering of two initially distant qubits, say, in distinct traps or in remote sites of a lattice, can be used to implement an entangling quantum gate betwe…

Martin Ringbauer and Rafael Chaves,

Quantum 1, 35 (2017). https://doi.org/10.22331/q-2017-11-25-35

Correlations between spacelike separated measurements on entangled quantum systems are stronger than any classical correlations and are at the heart of numerous quantum technologies. In prac…

Michalis Skotiniotis, Wolfgang Dür, and Pavel Sekatski,

Quantum 1, 34 (2017). https://doi.org/10.22331/q-2017-11-21-34

We consider fundamental limits on the detectable size of macroscopic quantum superpositions. We argue that a full quantum mechanical treatment of system plus measurement device is required,…

Thomas Van Himbeeck, Erik Woodhead, Nicolas J. Cerf, Raúl García-Patrón, and Stefano Pironio,

Quantum 1, 33 (2017). https://doi.org/10.22331/q-2017-11-18-33

The semi-device-independent approach provides a framework for prepare-and-measure quantum protocols using devices whose behavior must not be characterized nor trusted, except for a single as…

Patrick P. Hofer,

Quantum 1, 32 (2017). https://doi.org/10.22331/q-2017-10-12-32

We develop a general framework to investigate fluctuations of non-commuting observables. To this end, we consider the Keldysh quasi-probability distribution (KQPD). This distribution provide…

Jeongwan Haah, Matthew B. Hastings, D. Poulin, and D. Wecker,

Quantum 1, 31 (2017). https://doi.org/10.22331/q-2017-10-03-31

We present an infinite family of protocols to distill magic states for $T$-gates that has a low space overhead and uses an asymptotic number of input magic states to achieve a given target e…

Aniello Lampo, Soon Hoe Lim, Miguel Ángel García-March, and Maciej Lewenstein,

Quantum 1, 30 (2017). https://doi.org/10.22331/q-2017-09-27-30

We study the dynamics of a quantum impurity immersed in a Bose-Einstein condensate as an open quantum system in the framework of the quantum Brownian motion model. We derive a generalized La…

Antoine Tilloy,

Quantum 1, 29 (2017). https://doi.org/10.22331/q-2017-09-19-29

Non-Markovian stochastic Schrödinger equations (NMSSE) are important tools in quantum mechanics, from the theory of open systems to foundations. Yet, in general, they are but formal objects:…

Debbie Leung and John Watrous,

Quantum 1, 28 (2017). https://doi.org/10.22331/q-2017-09-19-28

The qubit depolarizing channel with noise parameter $\eta$ transmits an input qubit perfectly with probability $1-\eta$, and outputs the completely mixed state with probability $\eta$. We sh…

Pavel Sekatski, Michalis Skotiniotis, Janek Kołodyński, and Wolfgang Dür,

Quantum 1, 27 (2017). https://doi.org/10.22331/q-2017-09-06-27

We establish general limits on how precise a parameter, e.g. frequency or the strength of a magnetic field, can be estimated with the aid of full and fast quantum control. We consider uncorr…

Stacey Jeffery and Shelby Kimmel,

Quantum 1, 26 (2017). https://doi.org/10.22331/q-2017-08-17-26

We give a new upper bound on the quantum query complexity of deciding $st$-connectivity on certain classes of planar graphs, and show the bound is sometimes exponentially better than previou…

Whei Yeap Suen, Jayne Thompson, Andrew J. P. Garner, Vlatko Vedral, and Mile Gu,

Quantum 1, 25 (2017). https://doi.org/10.22331/q-2017-08-11-25

The minimal memory required to model a given stochastic process – known as the statistical complexity – is a widely adopted quantifier of structure in complexity science. Here, we ask if qua…

Alastair Kay,

Quantum 1, 24 (2017). https://doi.org/10.22331/q-2017-08-10-24

The production of quantum states required for use in quantum protocols & technologies is studied by developing the tools to re-engineer a perfect state transfer spin chain so that a separabl…

Rafael Chaves, Daniel Cavalcanti, and Leandro Aolita,

Quantum 1, 23 (2017). https://doi.org/10.22331/q-2017-08-04-23

As with entanglement, different forms of Bell nonlocality arise in the multipartite scenario. These can be defined in terms of relaxations of the causal assumptions in local hidden-variable…

Paul Erker, Mario Krenn, and Marcus Huber,

Quantum 1, 22 (2017). https://doi.org/10.22331/q-2017-07-28-22

We derive a framework for quantifying entanglement in multipartite and high dimensional systems using only correlations in two unbiased bases. We furthermore develop such bounds in cases whe…

Mark E. Pearce, Earl T. Campbell, and Pieter Kok,

Quantum 1, 21 (2017). https://doi.org/10.22331/q-2017-07-26-21

Measurements of an object's temperature are important in many disciplines, from astronomy to engineering, as are estimates of an object's spatial configuration. We present the quantum optima…

A. Chia, T. Paterek, and L. C. Kwek,

Quantum 1, 19 (2017). https://doi.org/10.22331/q-2017-07-21-19

We define the hitting time for a model of continuous-time open quantum walks in terms of quantum jumps. Our starting point is a master equation in Lindblad form, which can be taken as the qu…

Yoshifumi Nakata, Christoph Hirche, Ciara Morgan, and Andreas Winter,

Quantum 1, 18 (2017). https://doi.org/10.22331/q-2017-07-21-18

We investigate decoupling, one of the most important primitives in quantum Shannon theory, by replacing the uniformly distributed random unitaries commonly used to achieve the protocol, with…

Manuel Gessner, Luca Pezzè, and Augusto Smerzi,

Quantum 1, 17 (2017). https://doi.org/10.22331/q-2017-07-14-17

We introduce a multi-mode squeezing coefficient to characterize entanglement in $N$-partite continuous-variable systems. The coefficient relates to the squeezing of collective observables in…

Thomas D. Galley and Lluis Masanes,

Quantum 1, 15 (2017). https://doi.org/10.22331/q-2017-07-14-15

The standard postulates of quantum theory can be divided into two groups: the first one characterizes the structure and dynamics of pure states, while the second one specifies the structure…