Related Experiment Video
Updated: Jun 26, 2026
06:42
Generation and Coherent Control of Pulsed Quantum Frequency Combs
Published on: June 8, 2018
Locally optimal control of quantum systems with strong feedback
1Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA.
Physical Review Letters
|December 31, 2008
Summary
Researchers identified optimal monitoring strategies to reduce quantum system entropy. This work provides the first fully optimal feedback protocol for a 3-state quantum system (qutrit).
Area of Science:
- Quantum information science
- Quantum control theory
Background:
- Continuous monitoring of quantum systems is crucial for control.
- Quantifying entropy reduction guides the development of effective feedback protocols.
Purpose of the Study:
- To identify observables that maximize entropy reduction during continuous monitoring.
- To derive optimal feedback protocols for high-purity quantum systems.
- To find the first fully optimal feedback protocol for a 3-state system.
Main Methods:
- Analysis of quantum systems under continuous monitoring.
- Derivation of locally optimal feedback protocols.
- Explicit calculation for systems up to N=4.
- Investigation of qutrit systems with equispaced eigenvalues.
Main Results:
- Identified all observables maximizing instantaneous entropy reduction.
- Derived explicit expressions for optimal strong feedback protocols for N <= 4.
- Demonstrated that for a qutrit, the locally optimal protocol is globally optimal for observables with equispaced eigenvalues.
Conclusions:
- The study provides a systematic method for finding optimal quantum feedback protocols.
- The results offer practical strategies for controlling quantum systems with high fidelity.
- A significant advancement in achieving fully optimal control for multi-state quantum systems.
Related Concept Videos
01:26Feedback control systems
Feedback control systems are categorized in various ways based on their design, analysis, and signal types.
Linear feedback systems are theoretical models that simplify analysis and design. These systems operate under the principle that their output is directly proportional to their input within certain ranges. For instance, an amplifier in a control system behaves linearly as long as the input signal remains within a specific range. However, most physical systems exhibit inherent nonlinearity...
Linear feedback systems are theoretical models that simplify analysis and design. These systems operate under the principle that their output is directly proportional to their input within certain ranges. For instance, an amplifier in a control system behaves linearly as long as the input signal remains within a specific range. However, most physical systems exhibit inherent nonlinearity...
01:23Root Loci for Positive-Feedback Systems
The Hartley oscillator is a positive feedback system that sustains oscillations by feeding the output back to the input in phase, thereby reinforcing the signal. Positive feedback systems can be viewed as negative feedback systems with inverted feedback signals. In these systems, the root locus encompasses all points on the s-plane where the angle of the system transfer function equals 360 degrees.
The construction rules for the root locus in positive feedback systems are similar to those in...
The construction rules for the root locus in positive feedback systems are similar to those in...
01:10Control Systems
Control systems are everywhere in contemporary society, influencing diverse applications from aerospace to automated manufacturing. These systems can be found naturally within biological processes, such as blood sugar regulation and heart rate adjustment in response to stress, as well as in man-made systems like elevators and automated vehicles. A control system is essentially a network of subsystems and processes that collaboratively convert specific inputs into desired outputs.
At the heart...
At the heart...
01:24Effects of feedback
Feedback in control systems plays a critical role in shaping various operational parameters, extending beyond simple error reduction to influence stability, bandwidth, gain, impedance, and sensitivity. Understanding these effects requires examining a basic feedback system characterized by defined input, output, error, and feedback signals.
Feedback significantly modifies the gain of a control system. The gain of a system without feedback is altered by a factor of one plus GH, where G represents...
Feedback significantly modifies the gain of a control system. The gain of a system without feedback is altered by a factor of one plus GH, where G represents...
01:17Open and closed-loop control systems
Control systems are foundational elements in automation and engineering. They are broadly categorized into open-loop and closed-loop systems. These classifications hinge on the presence or absence of feedback mechanisms, significantly influencing the system's performance, complexity, and application.
An open-loop control system operates without feedback from the output. It consists of two primary elements: the controller and the controlled process. The controller receives an input signal and...
An open-loop control system operates without feedback from the output. It consists of two primary elements: the controller and the controlled process. The controller receives an input signal and...
01:14Conservation of Energy in Control Volume
Consider a turbine operating under steady-flow conditions. The control volume is drawn around the turbine, with fluid entering at one point and exiting at another. The turbine extracts energy from the fluid, which performs mechanical work (shaft work).
For steady flow systems, the time derivative of the stored energy becomes zero since there is no energy accumulation within the control volume. This simplifies the energy equation to:
For steady flow systems, the time derivative of the stored energy becomes zero since there is no energy accumulation within the control volume. This simplifies the energy equation to: