26 research outputs found
Experimental Demonstration of a Quantum Circuit using Linear Optics Gates
One of the main advantages of an optical approach to quantum computing is the
fact that optical fibers can be used to connect the logic and memory devices to
form useful circuits, in analogy with the wires of a conventional computer.
Here we describe an experimental demonstration of a simple quantum circuit of
that kind in which two probabilistic exclusive-OR (XOR) logic gates were
combined to calculate the parity of three input qubits.Comment: v2 is final PRA versio
Probabilistic Quantum Encoder for Single-Photon Qubits
We describe an experiment in which a physical qubit represented by the
polarization state of a single-photon was probabilistically encoded in the
logical state of two photons. The experiment relied on linear optics,
post-selection, and three-photon interference effects produced by a parametric
down-conversion photon pair and a weak coherent state. An interesting
consequence of the encoding operation was the ability to observe entangled
three-photon Greenberger-Horne-Zeilinger states.Comment: 4 pages, 4 figures; submitted to Phys. Rev.
Investigation of a single-photon source based on quantum interference
We report on an experimental investigation of a single-photon source based on
a quantum interference effect first demonstrated by Koashi, Matsuoka, and
Hirano [Phys. Rev. A 53, 3621 (1996)]. For certain types of measurement-based
quantum information processing applications this technique may be useful as a
high rate, but random, source of single photons.Comment: Submitted to the New J. Phys. Focus Issue on "Measurement-based
quantum information processing
Heralded Two-Photon Entanglement from Probabilistic Quantum Logic Operations on Multiple Parametric Down-Conversion Sources
An ideal controlled-NOT gate followed by projective measurements can be used
to identify specific Bell states of its two input qubits. When the input qubits
are each members of independent Bell states, these projective measurements can
be used to swap the post-selected entanglement onto the remaining two qubits.
Here we apply this strategy to produce heralded two-photon polarization
entanglement using Bell states that originate from independent parametric
down-conversion sources, and a particular probabilistic controlled-NOT gate
that is constructed from linear optical elements. The resulting implementation
is closely related to an earlier proposal by Sliwa and Banaszek
[quant-ph/0207117], and can be intuitively understood in terms of familiar
quantum information protocols. The possibility of producing a ``pseudo-demand''
source of two-photon entanglement by storing and releasing these heralded pairs
from independent cyclical quantum memory devices is also discussed.Comment: 5 pages, 4 figures; submitted to IEEE Journal of Selected Topics in
Quantum Electronics, special issue on "Quantum Internet Technologies
Quantum relays and noise suppression using linear optics
Probabilistic quantum non-demolition (QND) measurements can be performed
using linear optics and post-selection. Here we show how QND devices of this
kind can be used in a straightforward way to implement a quantum relay, which
is capable of extending the range of a quantum cryptography system by
suppressing the effects of detector noise. Unlike a quantum repeater, a quantum
relay system does not require entanglement purification or the ability to store
photons.Comment: minor changes; references adde
All-Optical Switching Demonstration using Two-Photon Absorption and the Classical Zeno Effect
Low-contrast all-optical Zeno switching has been demonstrated in a silicon
nitride microdisk resonator coupled to a hot atomic vapor. The device is based
on the suppression of the field build-up within a microcavity due to
non-degenerate two-photon absorption. This experiment used one beam in a
resonator and one in free-space due to limitations related to device physics.
These results suggest that a similar scheme with both beams resonant in the
cavity would correspond to input power levels near 20 nW.Comment: 4 pages, 5 figure