1,579,944 research outputs found
Different Traces of Quantum Systems Having the Same Classical Limit
Many quantum systems may have the same classical limit. We argue that in the
classical limit their traces do not necessarily converge one to another. The
trace formula allows to express quantum traces by means of classical quantities
as sums over periodic orbits of the classical system. To explain the lack of
convergence of the traces we need the quantum corrections to the classical
actions of periodic orbits. The four versions of the quantum baker map on the
sphere serve as an illustration of this problem.Comment: LaTeX 4 pages, 2 figures included, final published versio
Locking classical correlation in quantum states
We show that there exist bipartite quantum states which contain large hidden
classical correlation that can be unlocked by a disproportionately small amount
of classical communication. In particular, there are -qubit states for
which a one bit message doubles the optimal classical mutual information
between measurement results on the subsystems, from bits to bits.
States exhibiting this behavior need not be entangled. We study the range of
states exhibiting this phenomenon and bound its magnitude.Comment: 7 pages, revtex
Semiclassical Ehrenfest Paths
Trajectories are a central concept in our understanding of classical
phenomena and also in rationalizing quantum mechanical effects. In this work we
provide a way to determine semiclassical paths, approximations to quantum
averages in phase space, directly from classical trajectories. We avoid the
need of intermediate steps, like particular solutions to the Schroedinger
equation or numerical integration in phase space by considering the system to
be initially in a coherent state and by assuming that its early dynamics is
governed by the Heller semiclassical approximation. Our result is valid for
short propagation times only, but gives non-trivial information on the
quantum-classical transition.Comment: To appear in Physics Letters
Decoherence as a sequence of entanglement swaps
Standard semi-classical models of decoherence do not take explicit account of
the classical information required to specify the system - environment
boundary. I show that this information can be represented as a finite set of
reference eigenvalues that must be encoded by any observer, including any
apparatus, able to distinguish the system from its environment. When the
information required for system identification is accounted for in this way,
decoherence can be described as a sequence of entanglement swaps between
reference and pointer components of the system and their respective
environments. Doing so removes the need for the a priori assumptions of ontic
boundaries required by semi-classical models.Comment: 13 pgs, 3 figures. Accepted by Results in Physic
Quantum-enhanced Secure Delegated Classical Computing
We present a quantumly-enhanced protocol to achieve unconditionally secure
delegated classical computation where the client and the server have both
limited classical and quantum computing capacity. We prove the same task cannot
be achieved using only classical protocols. This extends the work of Anders and
Browne on the computational power of correlations to a security setting.
Concretely, we present how a client with access to a non-universal classical
gate such as a parity gate could achieve unconditionally secure delegated
universal classical computation by exploiting minimal quantum gadgets. In
particular, unlike the universal blind quantum computing protocols, the
restriction of the task to classical computing removes the need for a full
universal quantum machine on the side of the server and makes these new
protocols readily implementable with the currently available quantum technology
in the lab
Quantization of Light Energy Directly from Classical Electromagnetic Theory in Vacuum
It is currently believed that light quantum or the quantization of light
energy is beyond classical physics and the picture of wave-particle duality,
which was criticized by Einstein but attracted a number of experimental
researches, is necessary for the description of light. We show in this paper,
however, that the quantization of light energy in vacuum, which is the same as
that in quantum electrodynamics, can be derived directly from the classical
electromagnetic theory through the consideration of statistics based on
classical physics. Therefore, the quantization of energy is an intrinsic
property of light as a classical electromagnetic wave and has no need of being
related to particles.Comment: 9 pages, 1 figur
Strong converse rates for classical communication over thermal and additive noise bosonic channels
We prove that several known upper bounds on the classical capacity of thermal
and additive noise bosonic channels are actually strong converse rates. Our
results strengthen the interpretation of these upper bounds, in the sense that
we now know that the probability of correctly decoding a classical message
rapidly converges to zero in the limit of many channel uses if the
communication rate exceeds these upper bounds. In order for these theorems to
hold, we need to impose a maximum photon number constraint on the states input
to the channel (the strong converse property need not hold if there is only a
mean photon number constraint). Our first theorem demonstrates that Koenig and
Smith's upper bound on the classical capacity of the thermal bosonic channel is
a strong converse rate, and we prove this result by utilizing the structural
decomposition of a thermal channel into a pure-loss channel followed by an
amplifier channel. Our second theorem demonstrates that Giovannetti et al.'s
upper bound on the classical capacity of a thermal bosonic channel corresponds
to a strong converse rate, and we prove this result by relating success
probability to rate, the effective dimension of the output space, and the
purity of the channel as measured by the Renyi collision entropy. Finally, we
use similar techniques to prove that similar previously known upper bounds on
the classical capacity of an additive noise bosonic channel correspond to
strong converse rates.Comment: Accepted for publication in Physical Review A; minor changes in the
text and few reference
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