6,406 research outputs found
Quantum Bit Commitment with a Composite Evidence
Entanglement-based attacks, which are subtle and powerful, are usually
believed to render quantum bit commitment insecure. We point out that the no-go
argument leading to this view implicitly assumes the evidence-of-commitment to
be a monolithic quantum system. We argue that more general evidence structures,
allowing for a composite, hybrid (classical-quantum) evidence, conduce to
improved security. In particular, we present and prove the security of the
following protocol: Bob sends Alice an anonymous state. She inscribes her
commitment by measuring part of it in the + (for ) or (for
) basis. She then communicates to him the (classical) measurement outcome
and the part-measured anonymous state interpolated into other, randomly
prepared qubits as her evidence-of-commitment.Comment: 6 pages, minor changes, journal reference adde
Helstrom Theorem by No-Signaling Condition
We prove a special case of Helstrom theorem by using no-signaling condition
in the special theory of relativity that faster-than-light communication is
impossible.Comment: Minor corrections (A reference added, discussion part deleted, typos
in equations corrected), 2 pages, RevTe
Quantum Noise Randomized Ciphers
We review the notion of a classical random cipher and its advantages. We
sharpen the usual description of random ciphers to a particular mathematical
characterization suggested by the salient feature responsible for their
increased security. We describe a concrete system known as AlphaEta and show
that it is equivalent to a random cipher in which the required randomization is
effected by coherent-state quantum noise. We describe the currently known
security features of AlphaEta and similar systems, including lower bounds on
the unicity distances against ciphertext-only and known-plaintext attacks. We
show how AlphaEta used in conjunction with any standard stream cipher such as
AES (Advanced Encryption Standard) provides an additional, qualitatively
different layer of security from physical encryption against known-plaintext
attacks on the key. We refute some claims in the literature that AlphaEta is
equivalent to a non-random stream cipher.Comment: Accepted for publication in Phys. Rev. A; Discussion augmented and
re-organized; Section 5 contains a detailed response to 'T. Nishioka, T.
Hasegawa, H. Ishizuka, K. Imafuku, H. Imai: Phys. Lett. A 327 (2004) 28-32
/quant-ph/0310168' & 'T. Nishioka, T. Hasegawa, H. Ishizuka, K. Imafuku, H.
Imai: Phys. Lett. A 346 (2005) 7
Maine Distributed Solar Valuation Study
During its 2014 session, the Maine Legislature enacted an Act to Support Solar Energy Development in Maine. P.L Chapter 562 (April 24, 2014) (codified at 35‐A M.R.S. §§ 3471‐3473) (“Act”). Section 1 of the Act contains the Legislative finding that it is in the public interest is to develop renewable energy resources, including solar energy, in a manner that protects and improves the health and well‐being of the citizens and natural environment of the State while also providing economic benefits to communities, ratepayers and the overall economy of the State.
Section 2 of the Act requires the Public Utilities Commission (Commission) to determine the value of distributed solar energy generation in the State, evaluate implementation options, and to deliver a report to the Legislature. To support this work, the Commission engaged a project team comprising Clean Power Research (Napa, California), Sustainable Energy Advantage (Framingham, Massachusetts), Pace Energy and Climate Center at the Pace Law School (White Plains, New York), and Dr. Richard Perez (Albany, New York).
Under the project, the team developed the methodology under a Commission‐run stakeholder review process, conducted a valuation on distributed solar for three utility territories, and developed a summary of implementation options for increasing deployment of distributed solar generation in the State.
The report includes three volumes which accompany this Executive Summary: Volume I Methodology; Volume II Valuation Results; Volume III Implementation Options
Phase-covariant cloning of coherent states
We consider the problem of phase-covariant cloning for coherent states. We
show that an experimental scheme based on ideal phase measurement and
feedforward outperforms the semiclassical procedure of ideal phase measurement
and preparation in terms of fidelity. A realistic scheme where the ideal phase
measurement is replaced with double-homodyne detection is shown to be unable to
overcome the semiclassical cloning strategy. On the other hand, such a
realistic scheme is better than semiclassical cloning based on double-homodyne
phase measurement and preparation.Comment: 6 pages, 2 figures; updated references and minor corrections; in
press on Physical Review
Unified Treatment of Heterodyne Detection: the Shapiro-Wagner and Caves Frameworks
A comparative study is performed on two heterodyne systems of photon
detectors expressed in terms of a signal annihilation operator and an image
band creation operator called Shapiro-Wagner and Caves' frame, respectively.
This approach is based on the introduction of a convenient operator
which allows a unified formulation of both cases. For the Shapiro-Wagner
scheme, where , quantum phase and amplitude
are exactly defined in the context of relative number state (RNS)
representation, while a procedure is devised to handle suitably and in a
consistent way Caves' framework, characterized by , within the approximate simultaneous measurements of
noncommuting variables. In such a case RNS phase and amplitude make sense only
approximately.Comment: 25 pages. Just very minor editorial cosmetic change
Minimum-error discrimination between symmetric mixed quantum states
We provide a solution of finding optimal measurement strategy for
distinguishing between symmetric mixed quantum states. It is assumed that the
matrix elements of at least one of the symmetric quantum states are all real
and nonnegative in the basis of the eigenstates of the symmetry operator.Comment: 10 page
Does nonlinear metrology offer improved resolution? Answers from quantum information theory
A number of authors have suggested that nonlinear interactions can enhance
resolution of phase shifts beyond the usual Heisenberg scaling of 1/n, where n
is a measure of resources such as the number of subsystems of the probe state
or the mean photon number of the probe state. These suggestions are based on
calculations of `local precision' for particular nonlinear schemes. However, we
show that there is no simple connection between the local precision and the
average estimation error for these schemes, leading to a scaling puzzle. This
puzzle is partially resolved by a careful analysis of iterative implementations
of the suggested nonlinear schemes. However, it is shown that the suggested
nonlinear schemes are still limited to an exponential scaling in \sqrt{n}.
(This scaling may be compared to the exponential scaling in n which is
achievable if multiple passes are allowed, even for linear schemes.) The
question of whether nonlinear schemes may have a scaling advantage in the
presence of loss is left open.
Our results are based on a new bound for average estimation error that
depends on (i) an entropic measure of the degree to which the probe state can
encode a reference phase value, called the G-asymmetry, and (ii) any prior
information about the phase shift. This bound is asymptotically stronger than
bounds based on the variance of the phase shift generator. The G-asymmetry is
also shown to directly bound the average information gained per estimate. Our
results hold for any prior distribution of the shift parameter, and generalise
to estimates of any shift generated by an operator with discrete eigenvalues.Comment: 8 page
Minimum output entropy of bosonic channels: a conjecture
The von Neumann entropy at the output of a bosonic channel with thermal noise
is analyzed. Coherent-state inputs are conjectured to minimize this output
entropy. Physical and mathematical evidence in support of the conjecture is
provided. A stronger conjecture--that output states resulting from
coherent-state inputs majorize the output states from other inputs--is also
discussed.Comment: 15 pages, 12 figure
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