33,614 research outputs found
Advances in Sequential Measurement and Control of Open Quantum Systems
Novel concepts, perspectives and challenges in measuring and controlling an
open quantum system via sequential schemes are shown. We discuss how similar
protocols, relying both on repeated quantum measurements and dynamical
decoupling control pulses, can allow to: (i) Confine and protect quantum
dynamics from decoherence in accordance with the Zeno physics. (ii)
Analytically predict the probability that a quantum system is transferred into
a target quantum state by means of stochastic sequential measurements. (iii)
Optimally reconstruct the spectral density of environmental noise sources by
orthogonalizing in the frequency domain the filter functions driving the
designed quantum-sensor. The achievement of these tasks will enhance our
capability to observe and manipulate open quantum systems, thus bringing
advances to quantum science and technologies.Comment: 5 pages, v2: close to the published version. Proceeding presented at
the 11th Italian Quantum Information Science conference (IQIS2018), Catania,
Italy, 17-20 September 201
A short impossibility proof of Quantum Bit Commitment
Bit commitment protocols, whose security is based on the laws of quantum
mechanics alone, are generally held to be impossible on the basis of a
concealment-bindingness tradeoff. A strengthened and explicit impossibility
proof has been given in: G. M. D'Ariano, D. Kretschmann, D. Schlingemann, and
R. F. Werner, Phys. Rev. A 76, 032328 (2007), in the Heisenberg picture and in
a C*-algebraic framework, considering all conceivable protocols in which both
classical and quantum information are exchanged. In the present paper we
provide a new impossibility proof in the Schrodinger picture, greatly
simplifying the classification of protocols and strategies using the
mathematical formulation in terms of quantum combs, with each single-party
strategy represented by a conditional comb. We prove that assuming a stronger
notion of concealment--worst-case over the classical information
histories--allows Alice's cheat to pass also the worst-case Bob's test. The
present approach allows us to restate the concealment-bindingness tradeoff in
terms of the continuity of dilations of probabilistic quantum combs with
respect to the comb-discriminability distance.Comment: 15 pages, revtex
Flipping quantum coins
Coin flipping is a cryptographic primitive in which two distrustful parties
wish to generate a random bit in order to choose between two alternatives. This
task is impossible to realize when it relies solely on the asynchronous
exchange of classical bits: one dishonest player has complete control over the
final outcome. It is only when coin flipping is supplemented with quantum
communication that this problem can be alleviated, although partial bias
remains. Unfortunately, practical systems are subject to loss of quantum data,
which restores complete or nearly complete bias in previous protocols. We
report herein on the first implementation of a quantum coin-flipping protocol
that is impervious to loss. Moreover, in the presence of unavoidable
experimental noise, we propose to use this protocol sequentially to implement
many coin flips, which guarantees that a cheater unwillingly reveals
asymptotically, through an increased error rate, how many outcomes have been
fixed. Hence, we demonstrate for the first time the possibility of flipping
coins in a realistic setting. Flipping quantum coins thereby joins quantum key
distribution as one of the few currently practical applications of quantum
communication. We anticipate our findings to be useful for various
cryptographic protocols and other applications, such as an online casino, in
which a possibly unlimited number of coin flips has to be performed and where
each player is free to decide at any time whether to continue playing or not.Comment: 17 pages, 3 figure
The Quantum Internet
Quantum networks offer a unifying set of opportunities and challenges across
exciting intellectual and technical frontiers, including for quantum
computation, communication, and metrology. The realization of quantum networks
composed of many nodes and channels requires new scientific capabilities for
the generation and characterization of quantum coherence and entanglement.
Fundamental to this endeavor are quantum interconnects that convert quantum
states from one physical system to those of another in a reversible fashion.
Such quantum connectivity for networks can be achieved by optical interactions
of single photons and atoms, thereby enabling entanglement distribution and
quantum teleportation between nodes.Comment: 15 pages, 6 figures Higher resolution versions of the figures can be
downloaded from the following link:
http://www.its.caltech.edu/~hjkimble/QNet-figures-high-resolutio
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