13,688 research outputs found
Bounding and Estimating the Classical Information Rate of Quantum Channels with Memory
We consider the scenario of classical communication over a finite-dimensional
quantum channel with memory using a separable-state input ensemble and local
output measurements. We propose algorithms for estimating the information rate
of such communication setups, along with algorithms for bounding the
information rate based on so-called auxiliary channels. Some of the algorithms
are extensions of their counterparts for (classical) finite-state-machine
channels. Notably, we discuss suitable graphical models for doing the relevant
computations. Moreover, the auxiliary channels are learned in a data-driven
approach; i.e., only input/output sequences of the true channel are needed, but
not the channel model of the true channel.Comment: This work has been submitted to the IEEE Transactions on Information
Theory for possible publication. Copyright may be transferred without notice,
after which this version may no longer be accessibl
Security proof of quantum key distribution with detection efficiency mismatch
In theory, quantum key distribution (QKD) offers unconditional security based
on the laws of physics. However, as demonstrated in recent quantum hacking
theory and experimental papers, detection efficiency loophole can be fatal to
the security of practical QKD systems. Here, we describe the physical origin of
detection efficiency mismatch in various domains including spatial, spectral,
and time domains and in various experimental set-ups. More importantly, we
prove the unconditional security of QKD even with detection efficiency
mismatch. We explicitly show how the key generation rate is characterized by
the maximal detection efficiency ratio between the two detectors. Furthermore,
we prove that by randomly switching the bit assignments of the detectors, the
effect of detection efficiency mismatch can be completely eliminated.Comment: 35 pages, 7 figure
Digital quantum simulation of lattice gauge theories in three spatial dimensions
In the present work, we propose a scheme for digital formulation of lattice
gauge theories with dynamical fermions in 3+1 dimensions. All interactions are
obtained as a stroboscopic sequence of two-body interactions with an auxiliary
system. This enables quantum simulations of lattice gauge theories where the
magnetic four-body interactions arising in two and more spatial dimensions are
obtained without the use of perturbation theory, thus resulting in stronger
interactions compared with analogue approaches. The simulation scheme is
applicable to lattice gauge theories with either compact or finite gauge
groups. The required bounds on the digitization errors in lattice gauge
theories, due to the sequential nature of the stroboscopic time evolution, are
provided. Furthermore, an implementation of a lattice gauge theory with a
non-abelian gauge group, the dihedral group , is proposed employing the
aforementioned simulation scheme using ultracold atoms in optical lattices.Comment: 38 pages, 5 figure
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