16 research outputs found
Approaches to Single Photon Detection
We present recent results on our development of single photon detectors,
including: gated and free-running InGaAs/InP avalanche photodiodes; hybrid
detection systems based on sum-frequency generation and Si APDs; and SSPDs
(superconducting single photon detectors), for telecom wavelengths; as well as
SiPM (Silicon photomultiplier) detectors operating in the visible regime.Comment: NDIP08 Conf proceedings. 4 pages, 4 figure
Entanglement detection via condition of quantum correlation
We develop a novel necessary condition of quantum correlation. It is utilized
to construct -level bipartite Bell-type inequality which is strongly
resistant to noise and requires only analyses of measurement outcomes
compared to the previous result . Remarkably, a connection between
the arbitrary high-dimensional bipartite Bell-type inequality and entanglement
witnesses is found. Through the necessary condition of quantum correlation, we
propose that the witness operators to detect truly multipartite entanglement
for a generalized Greenberger-Horne-Zeilinger (GHZ) state with two local
measurement settings and a four-qubit singlet state with three settings.
Moreover, we also propose the first robust entanglement witness to detect
four-level tripartite GHZ state with only two local measurement settings
Preparation of polarization entangled mixed states of two photons
We propose a scheme for preparing arbitrary two photons polarization
entangled mixed states via controlled location decoherence. The scheme uses
only linear optical devices and single-mode optical fibers, and may be feasible
in experiment within current optical technology.Comment: 3 pages, 5 figs. The article has been rewritten. Discussion about
experiment are added. To appear in Phys. Rev.
Collective vs local measurements in qubit mixed state estimation
We discuss the problem of estimating a general (mixed) qubit state. We give
the optimal guess that can be inferred from any given set of measurements. For
collective measurements and for a large number of copies, we show that the
error in the estimation goes as 1/N. For local measurements we focus on the
simpler case of states lying on the equatorial plane of the Bloch sphere. We
show that standard tomographic techniques lead to an error proportional to
, while with our optimal data processing it is proportional to
.Comment: 4 pages, 1 figure, minor style changes, refs. adde
Experimental preparation of Werner state via spontaneous parametric down-conversion
We present an experiment of preparing Werner state via spontaneous parametric
down-conversion and controlled decoherence of photons in this paper. In this
experiment two independent BBO (beta-barium borate) crystals are used to
produce down-conversion light beams, which are mixed to prepare Werner state.Comment: 6 pages, 4 figures and 2 table
Experimental Entanglement Concentration and Universal Bell-state Synthesizer
We report a novel Bell-state synthesizer in which an interferometric
entanglement concentration scheme is used. An initially mixed polarization
state from type-II spontaneous parametric down-conversion becomes entangled
after the interferometric entanglement concentrator. This Bell-state
synthesizer is universal in the sense that the output polarization state is not
affected by spectral filtering, crystal thickness, and, most importantly, the
choice of pump source. It is also robust against environmental disturbance and
a more general state, partially mixedpartially entangled state, can be
readily generated as well.Comment: Minor update (Newer data
Measurement-induced nonlinearity in linear optics
Published versio
Quantum entanglement with acousto-optic modulators: 2-photon beatings and Bell experiments with moving beamsplitters
We present an experiment testing quantum correlations with frequency shifted
photons. We test Bell inequality with 2-photon interferometry where we replace
the beamsplitters by acousto-optic modulators, which are equivalent to moving
beamsplitters. We measure the 2-photon beatings induced by the frequency
shifts, and we propose a cryptographic scheme in relation. Finally, setting the
experiment in a relativistic configuration, we demonstrate that the quantum
correlations are not only independent of the distance but also of the time
ordering between the two single-photon measurements.Comment: 14 pages, 16 figure
Inferring superposition and entanglement from measurements in a single basis
We discuss what can be inferred from measurements on one- and two-qubit
systems using a single measurement basis at various times. We show that, given
reasonable physical assumptions, carrying out such measurements at
quarter-period intervals is enough to demonstrate coherent oscillations of one
or two qubits between the relevant measurement basis states. One can thus infer
from such measurements alone that an approximately equal superposition of two
measurement basis states has been created in a coherent oscillation experiment.
Similarly, one can infer that a near maximally entangled state of two qubits
has been created in an experiment involving a putative SWAP gate. These results
apply even if the relevant quantum systems are only approximate qubits. We
discuss applications to fundamental quantum physics experiments and quantum
information processing investigations.Comment: Final published versio
Comparing different approaches for generating random numbers device-independently using a photon pair source
10.1088/1367-2630/17/2/023023New Journal of Physics1