202,541 research outputs found
Quantum control, quantum information processing, and quantum-limited metrology with trapped ions
We briefly discuss recent experiments on quantum information processing using
trapped ions at NIST. A central theme of this work has been to increase our
capabilities in terms of quantum computing protocols, but we have also applied
the same concepts to improved metrology, particularly in the area of frequency
standards and atomic clocks. Such work may eventually shed light on more
fundamental issues, such as the quantum measurement problem.Comment: Proceedings of the International Conference on Laser Spectroscopy
(ICOLS), 10 pages, 5 figure
NMR Techniques for Quantum Control and Computation
Fifty years of developments in nuclear magnetic resonance (NMR) have resulted
in an unrivaled degree of control of the dynamics of coupled two-level quantum
systems. This coherent control of nuclear spin dynamics has recently been taken
to a new level, motivated by the interest in quantum information processing.
NMR has been the workhorse for the experimental implementation of quantum
protocols, allowing exquisite control of systems up to seven qubits in size.
Here, we survey and summarize a broad variety of pulse control and tomographic
techniques which have been developed for and used in NMR quantum computation.
Many of these will be useful in other quantum systems now being considered for
implementation of quantum information processing tasks.Comment: 33 pages, accepted for publication in Rev. Mod. Phys., added
subsection on T_{1,\rho} (V.A.6) and on time-optimal pulse sequences
(III.A.6), redid some figures, made many small changes, expanded reference
Quantum Computing, Metrology, and Imaging
Information science is entering into a new era in which certain subtleties of
quantum mechanics enables large enhancements in computational efficiency and
communication security. Naturally, precise control of quantum systems required
for the implementation of quantum information processing protocols implies
potential breakthoughs in other sciences and technologies. We discuss recent
developments in quantum control in optical systems and their applications in
metrology and imaging.Comment: 11 pages, 6 figures; Proceedings of SPIE: Fluctuations and Noise in
Photonics and Quantum Optics III (2005
Automated tuning of inter-dot tunnel couplings in quantum dot arrays
Semiconductor quantum dot arrays defined electrostatically in a 2D electron
gas provide a scalable platform for quantum information processing and quantum
simulations. For the operation of quantum dot arrays, appropriate voltages need
to be applied to the gate electrodes that define the quantum dot potential
landscape. Tuning the gate voltages has proven to be a time-consuming task,
because of initial electrostatic disorder and capacitive cross-talk effects.
Here, we report on the automated tuning of the inter-dot tunnel coupling in a
linear array of gate-defined semiconductor quantum dots. The automation of the
tuning of the inter-dot tunnel coupling is the next step forward in scalable
and efficient control of larger quantum dot arrays. This work greatly reduces
the effort of tuning semiconductor quantum dots for quantum information
processing and quantum simulation
Dynamics and Control of a Quasi-1D Spin System
We study experimentally a system comprised of linear chains of spin-1/2
nuclei that provides a test-bed for multi-body dynamics and quantum information
processing. This system is a paradigm for a new class of quantum information
devices that can perform particular tasks even without universal control of the
whole quantum system. We investigate the extent of control achievable on the
system with current experimental apparatus and methods to gain information on
the system state, when full tomography is not possible and in any case highly
inefficient
Mismatched Quantum Filtering and Entropic Information
Quantum filtering is a signal processing technique that estimates the
posterior state of a quantum system under continuous measurements and has
become a standard tool in quantum information processing, with applications in
quantum state preparation, quantum metrology, and quantum control. If the
filter assumes a nominal model that differs from reality, however, the
estimation accuracy is bound to suffer. Here I derive identities that relate
the excess error caused by quantum filter mismatch to the relative entropy
between the true and nominal observation probability measures, with one
identity for Gaussian measurements, such as optical homodyne detection, and
another for Poissonian measurements, such as photon counting. These identities
generalize recent seminal results in classical information theory and provide
new operational meanings to relative entropy, mutual information, and channel
capacity in the context of quantum experiments.Comment: v1: first draft, 8 pages, v2: added introduction and more results on
mutual information and channel capacity, 12 pages, v3: minor updates, v4:
updated the presentatio
Photonic crystal chips for optical communications and quantum information processing
We discuss recent our recent progress on functional photonic crystals devices and circuits for classical and quantum information processing. For classical applications, we have demonstrated a room-temperature-operated, low threshold, nanocavity laser with pulse width in the picosecond regime; and an all-optical switch controlled with 60 fJ pulses that shows switching time on the order of tens of picoseconds. For quantum information processing, we discuss the promise of quantum networks on multifunctional photonic crystals chips. We also discuss a new coherent probing technique of quantum dots coupled to photonic crystal nanocavities and demonstrate amplitude and phase nonlinearities realized with control beams at the single photon level
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