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IFAC Proceedings Volumes

Control of Some Quantum Systems - Role of Phases

Viswanath Ramakrishna, Raimund J. Ober, HERSCHEL A. RABITZ

Published Jul 1, 2001• 0 citations
Publisher
DOI
10.1016/s1474-6670(17)35387-9

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The ability of an environment to assist in one-photon phase control relies upon entanglement between the system and bath and on the breaking of the time reversal symmetry. Here, one-photon phase control is examined analytically and numerically in a model system, allowing an analysis of the relative strength of these contributions. Further, the significant role of non-Markovian dynamics and of moderate system-bath coupling in enhancing one-photon phase control is demonstrated, and an explicit role for quantum mechanics is noted in the existence of initial non-zero stationary coherences. Finally, desirable conditions are shown to be required to observe such environmentally assisted control, since the system will naturally equilibrate with its environment at longer times, ultimately resulting in the loss of phase control.
The ability of an environment to assist in one-photon phase control relies upon entanglement between the system and bath and on the breaking of the time reversal symmetry. Here, one photon phase control is examined analytically and numerically in a model system, allowing an analysis of the relative strength of these contributions. Further, the significant role of non-Markovian dynamics and of moderate system-bath coupling in enhancing one-photon phase control is demonstrated, and an explicit role for quantum mechanics is noted in the existence of initial non-zero stationary coherences. Finally, desirable conditions are shown to be required to observe such environmentally assisted control, since the system will naturally equilibrate with its environment at longer times, ultimately resulting in the loss of phase control. 1 ar
The invention relates to calibration, validation, and control of a quantum system, such as a quantum processor, a quantum sensor, or a quantum measurement apparatus. More particularly, the invention provides a computer-implemented method and system for determining whether a phase-offset and/or phase-lag indicator derived from at least two observation streams is sufficiently identifiable for use in inference and/or parameter update. Rather than permitting direct use of the indicator once computed, the invention requires passage of a machine-enforceable identifiability gate Iφ before the indicator is admitted for downstream use. In preferred implementations, the method defines at least a first measurement role and a second measurement role, acquires observation data under the two roles according to a role-activation schedule that prevents simultaneous access within the same acquisition step, and computes at least one phase-offset/phase-lag indicator over a candidate lag window. The identifiability gate Iφ then applies multiple technical checks, including calibration or estimation of acquisition-chain latency, instrument swap and/or acquisition-chain swap to test invariance of the indicator, at least one negative control, and explicit failure criteria for declaring the indicator not identifiable. Only when the indicator passes the gate is it used to generate a validated output and to update at least one control, acquisition, or signal pre-processing parameter of the quantum system. Upon failure of the gate, any parameter update based on the indicator is blocked and diagnostic data are output. In more specific embodiments, role switching is accepted only when predefined micro-invariants Q are preserved within tolerance, and a Van-proxy role-switch action is selected only if it passes a Van-proxy audit configured to reject actions that perturb relevant micro-dynamics of the quantum system. Additional embodiments may employ an adaptive role-activation schedule, a macro-entropy-based drift or instability signal, a frozen configuration manifest with version-specific hash binding, and a parameter-update lock that remains active until a new identifiability cycle passes after drift or failure. The invention thereby reduces artifact-driven parameter updates, improves robustness against acquisition-chain asymmetry and processing artifacts, and provides controlled requalification before re-enabling update.