Optimized state-discrimination receiver strategies for nonorthogonal states can improve the capacity of the
communication channels operating with error rates below the ones corresponding to conventional receivers.
Coherent signal-nulling receivers use a local oscillator to null the signal state and perform the discrimination of the
signal from an alphabet of nonorthogonal states. We describe our study of signal nulling for signals encoded in
nonorthogonal phase states. The signal nulling discrimination setup is the first step for the experimental
investigation of different discrimination strategies for receivers of coherent multi-phase encoded signals.
We present a general quantum-mechanical formalism to describe photon-pair generation via four-wave mixing in a
Silicon-on-Insulator (SOI) microresonator. We also provide design principles for efficient photon-pair generation
in an SOI microresonator through numerical simulations. Ring-cavity designs are shown to have a much wider
dispersion-compensate frequency range than straight-cavity designs. Such on-chip quantum devices are highly
promising for future integrated quantum information processing.
We report on our efforts in integrating a source and detection system of photon pairs that have a high end-to-end system
efficiency. This requires combining appropriate detectors and photon pair sources. Preliminary measurements show
that an observed heralding efficiency of 65% for single photons is readily achieved.
We report the development of a fiber-based single-spatial-mode source of photon-pairs where the efficiency of extracting photon pairs is 14× higher than a previous implementation [16]. This critical improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs/(s nm mW). The source can be configured to generate entangled photon-pairs, characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without correcting for accidentals.
We present a systematic study of a correlated photon-pair source based on a periodically-poled KTiOPO4
(PPKTP) waveguide. The waveguide was fabricated on a KTiOPO4 crystal supporting type-II parametric
down-conversion. In addition, periodic poling was applied along the waveguide to quasi-phase-match the type-0
down-conversion process. The design pump wavelength is 532 nm, and the wavelengths of the down-converted,
correlated photons are around 900 nm and 1300 nm. We examine the two-photon correlation spectra and singlephoton
spectra at a variety of temperature and power settings for both type-0 and type II down-conversion
processes. Our study shows that the waveguide source has a number of advantages compared to its bulk-crystal
counterpart, including higher spectral brightness, narrower emission bandwidth and single spatial-mode output.
With greatly simplified engineering, this compact, highly efficient, low photon-loss, and cost-effective waveguide
source of correlated photon pairs is promising for future chip-scale quantum information processing applications.
We describe the generation of entangled and hyperentangled photon pairs using a microstructure-fiber Sagnac
interferometer, which is formed by a polarizing beam splitter and a highly nonlinear microstructure fiber twisted
by 90° from end to end. This interferometer allows two identical four-wave mixing processes to occur on the same
fiber principal axis, ensuring perfect spatial and temporal mode matching of the two four-wave mixing outputs
on the polarizing beam splitter to create entanglement over the entire four-wave mixing phase-matching spectral
range. With an average pump power of 220 μW, we measure a two-photon coincidence rate of 1 kHz with ▵λ =
0.9 nm. Two-photon interference visibilities exceed 91% for polarization-entangled photon pairs generated from
this source, and are > 84% for both time-bin and polarization degrees of freedom for hyperentangled photons,
all without subtracting accidental coincidences.
We describe the preparation of a high spectral brightness, broad wavelength coverage, single-spatial mode source of polarization-entangled photon pairs operated at room temperature. The source takes advantage of single-mode fiber optics, highly nonlinear microstructure fiber, judicious phase-matching, and the inherent stability provided by a Sagnac interferometer. With a modest average pump power (300 μW), we create all four Bell states with a detected two-photon coincidence rate of 7 kHz per bandwidth of 0.9 nm, in a spectral range of more than 20 nm.
We theoretically investigate the feasibility of using spectral hole burning in Pr3+:Y2SiO5 to prepare an ensemble
of Pr3+ ions with a spectral distribution optimized for use as a quantum memory for single-photon states. We
introduce figures of merit for the spectral distribution of the Pr3+ ions when used as a quantum-memory node
in a Duan-Lukin-Cirac-Zoller-type quantum-repeater scheme. Finally, we describe progress toward optimizing
the hole-burning sequence by using a computational model of the hole-burning process to calculate these figures
of merit over a wide range of parameters.
The gains of Four-wave mixing and Raman scattering in an optical fiber vary with wavelength. We use this wavelength variation to experimentally optimize the four-wave mixing relative to the Raman scattering, resulting in high photon coincidence rates and high coincidence/accidental contrast ratios. We obtain a photon coincidence rate of 53.7 kHz/mW/nm with a coincidence/accidental contrast of 10:1 in a 1.8 m microstructure fiber. We discuss the use of this fiber as a source for photon-counting detector efficiency calibrations.
We present a systematic experimental study of generating correlated photon pairs using a reversed degenerate four-wave mixing process. By overlapping a pair of parallel- (or cross-) polarized laser pump pulses at conjugate frequencies in a microstructure fiber, parallel- or (cross-) polarized correlated photon pairs are generated at the middle frequency. The generation rate of correlated photons by four-wave mixing with parallel-polarized laser pumps in a 1.8 meter microstructure fiber is comparable or higher than that of a parametric down conversion process in a bulk-crystal at similar pump power levels.
A series of experiments has been performed to investigate the interaction of intense laser pulses with cryogenic noble gas droplets. Understanding of the time scales for this interaction is important for optimization of extreme ultraviolet (EUV) sources for next-generation lithography that utilize laser-produced plasmas. The temporal character of the plasma formed by the irradiation of micron-sized argon and krypton droplets with intense 200-mJ, 100-ps laser pulses was investigated using a pump-probe scheme. The evolution of the droplet plasma was assessed by monitoring delay-dependent x-ray and EUV emission, and by imaging frequency-doubled probe light scattered from the interaction region. Depending on the spectral region of interest and the droplet characteristics, the effective plasma lifetime extends from a few hundred picoseconds to several nanoseconds. These results are explained in terms of the plasma expansion, excitation emission, and recombination emission time scales.
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