114,961 research outputs found
Quantum Switch for the Quantum Internet: Noiseless Communications through Noisy Channels
Counter-intuitively, quantum mechanics enables quantum particles to propagate
simultaneously among multiple space-time trajectories. Hence, a quantum
information carrier can travel through different communication channels in a
quantum superposition of different orders, so that the relative time-order of
the communication channels becomes indefinite. This is realized by utilizing a
quantum device known as quantum switch. In this paper, we investigate, from a
communication-engineering perspective, the use of the quantum switch within the
quantum teleportation process, one of the key functionalities of the Quantum
Internet. Specifically, a theoretical analysis is conducted to quantify the
performance gain that can be achieved by employing a quantum switch for the
entanglement distribution process within the quantum teleportation with respect
to the case of absence of quantum switch. This analysis reveals that, by
utilizing the quantum switch, the quantum teleportation is heralded as a
noiseless communication process with a probability that, remarkably and
counter-intuitively, increases with the noise levels affecting the
communication channels considered in the indefinite-order time combination.Comment: 14 pages, double colum
Performance analysis of quantum key distribution in underwater turbulence channels
The current literature on quantum key distribution is limited mainly to transmissions over fiber optic, atmospheric, or satellite links and is not directly applicable to underwater environments with different channel characteristics. In this paper, we analyze the quantum bit error rate (QBER) and secret key rate (SKR) performance of the well-known BB84 protocol in underwater channels. As a path loss model, we consider a modified version of the Beer-Lambert formula, which takes into account the effect of scattering. We derive a closed-form expression for the wave structure function to determine the average power transfer over a turbulent underwater path and use this to obtain an upper bound on QBER as well as a lower bound on SKR. Based on the derived bounds, we present the performance of the BB84 protocol in different water types including dear, coastal, and turbid and under different atmospheric conditions such as clear, hazy, and overcast. We further investigate the effect of system parameters such as aperture size and detector field of view on QBER and SKR performance metrics.TÜBİTA
Vetoes for Inspiral Triggers in LIGO Data
Presented is a summary of studies by the LIGO Scientific Collaboration's
Inspiral Analysis Group on the development of possible vetoes to be used in
evaluation of data from the first two LIGO science data runs. Numerous
environmental monitor signals and interferometer control channels have been
analyzed in order to characterize the interferometers' performance. The results
of studies on selected data segments are provided in this paper. The vetoes
used in the compact binary inspiral analyses of LIGO's S1 and S2 science data
runs are presented and discussed.Comment: Submitted to Classical and Quantum Gravity for the GWDAW-8
proceeding
Quantum reading of digital memory with non-Gaussian entangled light
It has been shown recently (Phys. Rev. Lett. 106, 090504 (2011)) that
entangled light with Einstein-Podolsky-Rosen (EPR) correlations retrieves
information from digital memory better than any classical light. In identifying
this, a model of digital memory with each cell consisting of reflecting medium
with two reflectivities (each memory cell encoding the binary numbers 0 or 1)
is employed. The readout of binary memory essentially corresponds to
discrimination of two Bosonic attenuator channels characterized by different
reflectivities. The model requires an entire mathematical paraphernalia of
continuous variable Gaussian setting for its analysis, when arbitrary values of
reflectivities are considered. Here we restrict to a basic quantum read-out
mechanism with non-Gaussian entangled states of light, with the binary channels
to be discriminated being ideal memory characterized by reflectivity one i.e.,
an identity channel and thermal noise channel, where the signal light
illuminating the memory location gets completely lost (zero reflectivity) and
only a white thermal noise hitting the upper side of the memory reaches the
decoder. We compare the quantum reading efficiency of entangled light with any
classical source of light in this model. We show that entangled transmitters
offer better reading performance than any classical transmitters of light in
the regime of low signal intensity.Comment: 7 pages, 6 figures, To appear in Phys. Rev.
Improved Digital Quantum Simulation by Non-Unitary Channels
Simulating quantum systems is one of the most promising avenues to harness
the computational power of quantum computers. However, hardware errors in noisy
near-term devices remain a major obstacle for applications. Ideas based on the
randomization of Suzuki-Trotter product formulas have been shown to be a
powerful approach to reducing the errors of quantum simulation and lowering the
gate count. In this paper, we study the performance of non-unitary simulation
channels and consider the error structure of channels constructed from a
weighted average of unitary circuits. We show that averaging over just a few
simulation circuits can significantly reduce the Trotterization error for both
single-step short-time and multi-step long-time simulations. We focus our
analysis on two approaches for constructing circuit ensembles for averaging:
(i) permuting the order of the terms in the Hamiltonian and (ii) applying a set
of global symmetry transformations. We compare our analytical error bounds to
empirical performance and show that empirical error reduction surpasses our
analytical estimates in most cases. Finally, we test our method on an IonQ
trapped-ion quantum computer accessed via the Amazon Braket cloud platform, and
benchmark the performance of the averaging approach.Comment: 24 pages, 9 figure
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