12,469 research outputs found
Entanglement decoherence in a gravitational well according to the event formalism
The event formalism is a non-linear extension of quantum field theory
designed to be compatible with the closed time-like curves that appear in
general relativity. Whilst reducing to standard quantum field theory in flat
space-time the formalism leads to testably different predictions for
entanglement distribution in curved space. In this paper we introduce a more
general version of the formalism and use it to analyse the practicality of an
experimental test of its predictions in the earth's gravitational well
Optical Quantum Computation
We review the field of Optical Quantum Computation, considering the various
implementations that have been proposed and the experimental progress that has
been made toward realizing them. We examine both linear and nonlinear
approaches and both particle and field encodings. In particular we discuss the
prospects for large scale optical quantum computing in terms of the most
promising physical architectures and the technical requirements for realizing
them
High-Fidelity Z-Measurement Error Correction of Optical Qubits
We demonstrate a quantum error correction scheme that protects against
accidental measurement, using an encoding where the logical state of a single
qubit is encoded into two physical qubits using a non-deterministic photonic
CNOT gate. For the single qubit input states |0>, |1>, |0>+|1>, |0>-|1>,
|0>+i|1>, and |0>-i|1> our encoder produces the appropriate 2-qubit encoded
state with an average fidelity of 0.88(3) and the single qubit decoded states
have an average fidelity of 0.93(5) with the original state. We are able to
decode the 2-qubit state (up to a bit flip) by performing a measurement on one
of the qubits in the logical basis; we find that the 64 1-qubit decoded states
arising from 16 real and imaginary single qubit superposition inputs have an
average fidelity of 0.96(3).Comment: 4 pages, 4 figures, comments welcom
Phase estimation as a quantum nondemolition measurement
The phase estimation algorithm, which is at the heart of a variety of quantum
algorithms, including Shor's factoring algorithm, allows a quantum computer to
accurately determine an eigenvalue of an unitary operator. Quantum
nondemolition measurements are a quantum mechanical procedure, used to overcome
the standard quantum limit when measuring an observable. We show that the phase
estimation algorithm, in both the discrete and continuous variable setting, can
be viewed as a quantum nondemolition measurement.Comment: 4 pages, 2 figures, RevTeX
Loophole-free Bell test based on local precertification of photon's presence
A loophole-free violation of Bell inequalities is of fundamental importance
for demonstrating quantum nonlocality and long-distance device-independent
secure communication. However, transmission losses represent a fundamental
limitation for photonic loophole-free Bell tests. A local precertification of
the presence of the photons immediately before the local measurements may solve
this problem. We show that local precertification is feasible by integrating
three current technologies: (i) enhanced single-photon down-conversion to
locally create a flag photon, (ii) nanowire-based superconducting single-photon
detectors for a fast flag detection, and (iii) superconducting transition-edge
sensors to close the detection loophole. We carry out a precise space-time
analysis of the proposed scheme, showing its viability and feasibility.Comment: REVTeX4, 7 Pages, 1 figur
Quantum Computation with Coherent States, Linear Interactions and Superposed Resources
We show that quantum computation circuits with coherent states as the logical
qubits can be constructed using very simple linear networks, conditional
measurements and coherent superposition resource states
Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions
We report single-shot measurements of resistance versus time for thermally
assisted spin-torque-driven switching in magnetic tunnel junctions. We achieve
sufficient sensitivity to resolve the resistance signals leading up to
switching, including the variations between individual switching events.
Analyses of pre-switching thermal fluctuations allow detailed measurements of
coherence times and variations in magnetization precession amplitude. We find
that with a small in-plane hard-axis magnetic field the magnetization dynamics
are more spatially coherent than for the case of zero field.Comment: 13 pages, 4 figure
Communicating continuous quantum variables between different Lorentz frames
We show how to communicate Heisenberg-limited continuous (quantum) variables
between Alice and Bob in the case where they occupy two inertial reference
frames that differ by an unknown Lorentz boost. There are two effects that need
to be overcome: the Doppler shift and the absence of synchronized clocks.
Furthermore, we show how Alice and Bob can share Doppler-invariant
entanglement, and we demonstrate that the protocol is robust under photon loss.Comment: 4 pages, 1 figur
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