Rapid measurement and purification using quantum feedback control

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Author(s)
Primary Supervisor
Wiseman, Howard
Other Supervisors
Jacobs, Kurt
Vaccaro, Joan
Year published
2010
Metadata
Show full item recordAbstract
I study the rate at which information can be extracted from a finite-dimensional open quantum system using the quantum trajectory description of a continuous measurement. I derive the rate at which information is extracted for a measurement without any control; this sets the benchmark to which the subsequent control protocols are compared. Next I consider control protocols that increase the rate of information extraction. The first such protocol applies feedback so the state and the measurement basis are unbiased at all times. The use of unbiased bases means that this protocol is essentially quantum mechanical in nature. For ...
View more >I study the rate at which information can be extracted from a finite-dimensional open quantum system using the quantum trajectory description of a continuous measurement. I derive the rate at which information is extracted for a measurement without any control; this sets the benchmark to which the subsequent control protocols are compared. Next I consider control protocols that increase the rate of information extraction. The first such protocol applies feedback so the state and the measurement basis are unbiased at all times. The use of unbiased bases means that this protocol is essentially quantum mechanical in nature. For observables with equally spaced eigenvalues, the “speed-up” in the information extraction afforded by unbiased basis feedback, is proportional to the square of the observed system’s Hilbert space. The second protocol considered optimally permutes the eigenvalues of the quantum state in the logical basis. As the measured observable and state commute at all times this protocol is essentially classical in nature. The speed-up provided by this protocol is also quadratic. The final protocol I consider is a new type of control. It merges open-loop quantum control and quantum filtering. This method also affords an improvement in the rate of information extraction.
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View more >I study the rate at which information can be extracted from a finite-dimensional open quantum system using the quantum trajectory description of a continuous measurement. I derive the rate at which information is extracted for a measurement without any control; this sets the benchmark to which the subsequent control protocols are compared. Next I consider control protocols that increase the rate of information extraction. The first such protocol applies feedback so the state and the measurement basis are unbiased at all times. The use of unbiased bases means that this protocol is essentially quantum mechanical in nature. For observables with equally spaced eigenvalues, the “speed-up” in the information extraction afforded by unbiased basis feedback, is proportional to the square of the observed system’s Hilbert space. The second protocol considered optimally permutes the eigenvalues of the quantum state in the logical basis. As the measured observable and state commute at all times this protocol is essentially classical in nature. The speed-up provided by this protocol is also quadratic. The final protocol I consider is a new type of control. It merges open-loop quantum control and quantum filtering. This method also affords an improvement in the rate of information extraction.
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Thesis Type
Thesis (PhD Doctorate)
Degree Program
Doctor of Philosophy (PhD)
School
School of Biomolecular and Physical Sciences
Copyright Statement
The author owns the copyright in this thesis, unless stated otherwise.
Item Access Status
Public
Note
Markup retained because his is a 'jump' link to chapter.
Subject
finite-dimensional open quantum system
Hilbert space
quantum control
quantum filtering