281 research outputs found
Quantum state reconstruction via continuous measurement
We present a new procedure for quantum state reconstruction based on weak
continuous measurement of an ensemble average. By applying controlled evolution
to the initial state new information is continually mapped onto the measured
observable. A Bayesian filter is then used to update the state-estimate in
accordance with the measurement record. This generalizes the standard paradigm
for quantum tomography based on strong, destructive measurements on separate
ensembles. This approach to state estimation can be non-destructive and
real-time, giving information about observables whose evolution cannot be
described classically, opening the door to new types of quantum feedback
control.Comment: 4 pages, 2 figure
Quantum Control of the Hyperfine Spin of a Cs Atom Ensemble
We demonstrate quantum control of a large spin-angular momentum associated
with the F=3 hyperfine ground state of 133Cs. A combination of time dependent
magnetic fields and a static tensor light shift is used to implement
near-optimal controls and map a fiducial state to a broad range of target
states, with yields in the range 0.8-0.9. Squeezed states are produced also by
an adiabatic scheme that is more robust against errors. Universal control
facilitates the encoding and manipulation of qubits and qudits in atomic ground
states, and may lead to improvement of some precision measurements.Comment: 4 pages, 4 figures (color
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