334 research outputs found
Accurate Microwave Control and Real-Time Diagnostics of Neutral Atom Qubits
We demonstrate accurate single-qubit control in an ensemble of atomic qubits
trapped in an optical lattice. The qubits are driven with microwave radiation,
and their dynamics tracked by optical probe polarimetry. Real-time diagnostics
is crucial to minimize systematic errors and optimize the performance of
single-qubit gates, leading to fidelities of 0.99 for single-qubit pi
rotations. We show that increased robustness to large, deliberately introduced
errors can be achieved through the use of composite rotations. However, during
normal operation the combination of very small intrinsic errors and additional
decoherence during the longer pulse sequences precludes any significant
performance gain in our current experiment.Comment: 9 pages, 7 figure
Intrinsic Quantum Correlations of Weak Coherent States for Quantum Communication
Intrinsic quantum correlations of weak coherent states are observed between
two parties through a novel detection scheme, which can be used as a supplement
to the existence decoy-state BB84 and differential phase-shift quantum key
distribution (DPS-QKD) protocols. In a proof-of-principle experiment, we
generate bi-partite correlations of weak coherent states using weak local
oscillator fields in two spatially separated balanced homodyne detections. We
employ nonlinearity of post-measurement method to obtain the bi-partite
correlations from two single-field interferences at individual homodyne
measurement.
This scheme is then used to demonstrate bits correlations between two parties
over a distance of 10 km through a transmission fiber. We believe that the
scheme can add another physical layer of security to these protocols for
quantum key distribution.Comment: 10 pages, 4 figure
Optical Phase-Space-Time-Frequency Tomography
We present a new approach for constructing optical phase-space-time-frequency
tomography (OPSTFT) of an optical wave field. This tomography can be measured
by using a novel four-window optical imaging system based on two local
oscillator fields balanced heterodyne detection. The OPSTFT is a Wigner
distribution function of two independent Fourier Transform pairs, i.e.,
phase-space and time-frequency. From its theoretical and experimental aspects,
it can provide information of position, momentum, time and frequency of a
spatial light field with precision beyond the uncertainty principle. We
simulate the OPSTFT for a light field obscured by a wire and a single-line
absorption filter. We believe that the four-window system can provide spatial
and temporal properties of a wave field for quantum image processing and
biophotonics.Comment: 11 pages, 6 figure
Direct Measurement of Kirkwood-Rihaczek distribution for spatial properties of coherent light beam
We present direct measurement of Kirkwood-Rihaczek (KR) distribution for
spatial properties of coherent light beam in terms of position and momentum
(angle) coordinates. We employ a two-local oscillator (LO) balanced heterodyne
detection (BHD) to simultaneously extract distribution of transverse position
and momentum of a light beam. The two-LO BHD could measure KR distribution for
any complex wave field (including quantum mechanical wave function) without
applying tomography methods (inverse Radon transformation). Transformation of
KR distribution to Wigner, Glauber Sudarshan P- and Husimi or Q- distributions
in spatial coordinates are illustrated through experimental data. The direct
measurement of KR distribution could provide local information of wave field,
which is suitable for studying particle properties of a quantum system. While
Wigner function is suitable for studying wave properties such as interference,
and hence provides nonlocal information of the wave field. The method developed
here can be used for exploring spatial quantum state for quantum mapping and
computing, optical phase space imaging for biomedical applications.Comment: 27 pages, 14 figure
Photon-pair generation with a 100 nm thick carbon nanotube film
Nonlinear optics based on bulk materials is the current technique of choice for quantum-state generation and information processing. Scaling of nonlinear optical quantum devices is of significant interest to enable quantum devices with high performance. However, it is challenging to scale the nonlinear optical devices down to the nanoscale dimension due to relatively small nonlinear optical response of traditional bulk materials. Here, correlated photon pairs are generated in the nanometer scale using a nonlinear optical device for the first time. The approach uses spontaneous four-wave mixing in a carbon nanotube film with extremely large Kerr-nonlinearity (≈100 000 times larger than that of the widely used silica), which is achieved through careful control of the tube diameter during the carbon nanotube growth. Photon pairs with a coincidence to accidental ratio of 18 at the telecom wavelength of 1.5 μm are generated at room temperature in a ≈100 nm thick carbon nanotube film device, i.e., 1000 times thinner than the smallest existing devices. These results are promising for future integrated nonlinear quantum devices (e.g., quantum emission and processing devices)
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