16 research outputs found
Four-Photon Quantum Interferometry at a Telecom Wavelength
We report the experimental demonstration of four-photon quantum interference
using telecom-wavelength photons. Realization of multi-photon quantum
interference is essential to linear optics quantum information processing and
measurement-based quantum computing. We have developed a source that
efficiently emits photon pairs in a pure spectrotemporal mode at a telecom
wavelength region, and have demonstrated the quantum interference exhibiting
the reduced fringe intervals that correspond to the reduced de Broglie
wavelength of up to the four photon `NOON' state. Our result should open a path
to practical quantum information processing using telecom-wavelength photons.Comment: 4 pages, 4 figure
Generation of polarization entanglement from spatially-correlated photons in spontaneous parametric down-conversion
We propose a novel scheme to generate polarization entanglement from
spatially-correlated photon pairs. We experimentally realized a scheme by means
of a spatial correlation effect in a spontaneous parametric down-conversion and
a modified Michelson interferometer. The scheme we propose in this paper can be
interpreted as a conversion process from spatial correlation to polarization
entanglement.Comment: 4 pages, 4 figure
Coherent transfer of light polarization to electron spins in a semiconductor
We demonstrate that the superposition of light polarization states is
coherently transferred to electron spins in a semiconductor quantum well. By
using time-resolved Kerr rotation we observe the initial phase of Larmor
precession of electron spins whose coherence is transferred from light. To
break the electron-hole spin entanglement, we utilized the big discrepancy
between the transverse g-factors of electrons and light holes. The result
encourages us to make a quantum media converter between flying photon qubits
and stationary electron spin qubits in semiconductors.Comment: 4 pages. Submitted to Physical Review Letter
Theory of multiwave mixing and decoherence control in qubit array system
We develop a theory to analyze the decoherence effect in a charged qubit
array system with photon echo signals in the multiwave mixing configuration. We
present how the decoherence suppression effect by the {\it bang-bang} control
with the pulses can be demonstrated in laboratory by using a bulk
ensemble of exciton qubits and optical pulses whose pulse area is even smaller
than . Analysis is made on the time-integated multiwave mixing signals
diffracted into certain phase matching directions from a bulk ensemble.
Depending on the pulse interval conditions, the cross over from the decoherence
acceleration regime to the decoherence suppression regime, which is a peculiar
feature of the coherent interaction between a qubit and the reservoir bosons,
may be observed in the time-integated multiwave mixing signals in the realistic
case including inhomogeneous broadening effect. Our analysis will successfully
be applied to precise estimation of the reservoir parameters from experimental
data of the direction resolved signal intensities obtained in the multiwave
mixing technique.Comment: 19 pages, 11 figure
Experimental demonstration of quantum source coding
We report an experimental demonstration of Schumacher's quantum noiseless
coding theorem. Our experiment employs a sequence of single photons each of
which represents three qubits. We initially prepare each photon in one of a set
of 8 non-orthogonal codeword states corresponding to the value of a block of
three binary letters. We use quantum coding to compress this quantum data into
a two-qubit quantum channel and then uncompress the two-qubit channel to
restore the original data with a fidelity approaching the theoretical limit.Comment: 5 pages, 4 figure