Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Control of two qubit systems with Hamiltonian feedback

Charles D. Hill, David L. Goodwin, Jason F. Ralph

Published Mar 5, 2008• 0 citations
Publisher

Abstract

In this paper, we consider the control of two qubit systems in the presence of a weak measurement. In particular we consider how Hamiltonian feedback can be applied to two qubit systems, both in the case where only one qubit is measured, and in the case where a joint measurement is made of both qubits. We consider how the rate of entanglement can be increased by using a joint measurement and feedback, and also how information can be gathered about one qubit by measuring the other.

DOI
10.1117/12.777499

Related papers

Weak measurement and control of entanglement generation

Charles D. Hill, Jason F. Ralph

In this paper we show how weak measurement and local feedback can be used to control entanglement generation between two qubits. To do this, we make use of a decoherence free subspace. Weak measurement and feedback can be used to drive the system into this subspace rapidly. Once within the subspace, feedback can generate entanglement rapidly, or turn off entanglement generation dynamically. We also consider, in the context of weak measurement, some of the differences between purification and generating entanglement.

arXiv:0709.4217•Physical Review A•Jan 25, 2008•37 citations

Deterministic purity evolution via weak measurement for bipartite quantum systems

Charles D. Hill, Jason F. Ralph

In this paper we consider feedback control algorithms for the deterministic purification of a bipartite state consisting of two qubits, when the observer has access to only one of the qubits. We show that Hamiltonian feedback control can be used to produce deterministic evolution of the purity of either qubit individually, or both together.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jun 7, 2007•0 citations

Deterministic purity evolution via weak measurement for bipartite quantum systems

Charles D. Hill, Jason F. Ralph

In this paper we consider feedback control algorithms for the deterministic purification of a bipartite state consisting of two qubits, when the observer has access to only one of the qubits. We show that Hamiltonian feedback control can be used to produce deterministic evolution of the purity of either qubit individually, or both together.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jan 1, 2007•0 citations

Quantum control of a single qubit

Agata M. Brańczyk, Paulo E. M. F. Mendonça, Alexei Gilchrist +2 more

Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyze a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two nonorthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a nonprojective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement backaction. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realizes the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.

arXiv:quant-ph/0608037•Physical Review A•Jan 24, 2007•79 citations

Protecting Coherence and Entanglement by Quantum Feedback Controls

Jing Zhang, Re-Bing Wu, Chunwen Li +1 more

When a quantum system interacts with its environment, the so-called decoherence effect will normally destroy the coherence in the quantum state and the entanglement between its subsystems. We propose a feedback control strategy based on quantum weak measurements to protect coherence and entanglement of the quantum state against environmental disturbance. For a one-qubit quantum system under amplitude damping and dephasing decoherence channels, our strategy can preserve the coherence based on the measured information about the population difference between its two levels. For a two-qubit quantum system disentangled by independent amplitude damping and dephasing decoherence channels, the designed feedback control can preserve coherence between the ground state and the highest excited states by tuning the coupling strength between the two qubits, and at the same time minimize the loss of entanglement between the two qubits. As a consequence of dynamic symmetry, the generalization of these results derives the concept of control-induced decoherence-free observable subspace, for which several criteria are provided.

IEEE Transactions on Automatic Control•Jan 26, 2010•89 citations

Experimental Feedback Control of Quantum Systems Using Weak Measurements

Geoff Gillett, R. B. Dalton, B. P. Lanyon +7 more

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.

arXiv:0911.3698•Physical Review Letters•Feb 26, 2010•152 citations
In this paper, we consider the control of two qubit systems in the presence of a weak measurement. In particular we consider how Hamiltonian feedback can be applied to two qubit systems, both in the case where only one qubit is measured, and in the case where a joint measurement is made of both qubits. We consider how the rate of entanglement can be increased by using a joint measurement and feedback, and also how information can be gathered about one qubit by measuring the other.
In this paper we show how weak measurement and local feedback can be used to control entanglement generation between two qubits. To do this, we make use of a decoherence free subspace. Weak measurement and feedback can be used to drive the system into this subspace rapidly. Once within the subspace, feedback can generate entanglement rapidly, or turn off entanglement generation dynamically. We also consider, in the context of weak measurement, some of the differences between purification and generating entanglement.
Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyze a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two nonorthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a nonprojective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement backaction. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realizes the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.
When a quantum system interacts with its environment, the so-called decoherence effect will normally destroy the coherence in the quantum state and the entanglement between its subsystems. We propose a feedback control strategy based on quantum weak measurements to protect coherence and entanglement of the quantum state against environmental disturbance. For a one-qubit quantum system under amplitude damping and dephasing decoherence channels, our strategy can preserve the coherence based on the measured information about the population difference between its two levels. For a two-qubit quantum system disentangled by independent amplitude damping and dephasing decoherence channels, the designed feedback control can preserve coherence between the ground state and the highest excited states by tuning the coupling strength between the two qubits, and at the same time minimize the loss of entanglement between the two qubits. As a consequence of dynamic symmetry, the generalization of these results derives the concept of control-induced decoherence-free observable subspace, for which several criteria are provided.
A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.