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The Journal of Chemical Physics

Quantum amplifier: Measurement with entangled spins

Jae‐Seung Lee, Anatoly K. Khitrin

Published Aug 18, 2004• 18 citations
Publisher

Abstract

It is experimentally demonstrated that entangled quantum states can be used to amplify perturbations and to increase changes in observable values. The physical system is seven nuclear spins of single-labeled (13)C-benzene in a liquid crystalline matrix. An entangled state of six proton spins was used to monitor interaction with the (13)C spin.

DOI
10.1063/1.1788661

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Quantum Information Processing with Nuclear Spin-Based Devices

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This talk will illustrate the benefits offered by QIP with two devices which use quantum entanglement among nuclear spins to perform high-precision measurements: (1) a spin gyroscope that operates by detecting the frequency shift in the spins precession rate in the rotating frame, which is potentially more accurate than mechanical or optical devices; (2) a quantum amplifier which correlates the states of a macroscopic number of nuclear spins with the state of a single target spin, so that a collective measurement of the state of the amplifier’s spins reveals that of the target spin. Some potential implementations of these devices based on nuclear spins in naturally occurring materials will also be described.

TechConnect Briefs•May 8, 2005•0 citations
It is experimentally demonstrated that entangled quantum states can be used to amplify perturbations and to increase changes in observable values. The physical system is seven nuclear spins of single-labeled (13)C-benzene in a liquid crystalline matrix. An entangled state of six proton spins was used to monitor interaction with the (13)C spin.
It is experimentally demonstrated that an arbitrary quantum state of a single spin 1/2, a| upward arrow+b| downward arrow, can be converted into a superposition of the two ferromagnetic states of a spin cluster: a| upward arrow upward arrow... upward arrow upward arrow+b| downward arrow downward arrow... downward arrow downward arrow. The physical system is a cluster of seven dipolar-coupled nuclear spins of single-labeled 13C-benzene molecules in a liquid-crystalline matrix. In this complex system, the pseudopure ground state and the required controlled unitary transformations have been implemented. The experimental scheme can be considered as an explicit model of quantum measurement.
It is experimentally demonstrated that a quantum state, destroyed by uncontrollable natural decoherence, can be purified by using results of projective measurement and converted into a desired target pure state. The physical system is a cluster of seven dipolar-coupled nuclear spins of single-labelled 13 C-benzene in liquid crystal. 13 C spin plays the role of a device for measuring the protons' 'cat' state, a superposition of states with six spins up ( alive ) and six spins down ( dead ). Information about the state, stored in the 13 C spin, is used to bring the protons' subsystem into the target alive state, while the excess entropy produced by decoherence is transferred to the 'measuring device', the 13 C spin.
This talk will illustrate the benefits offered by QIP with two devices which use quantum entanglement among nuclear spins to perform high-precision measurements: (1) a spin gyroscope that operates by detecting the frequency shift in the spins precession rate in the rotating frame, which is potentially more accurate than mechanical or optical devices; (2) a quantum amplifier which correlates the states of a macroscopic number of nuclear spins with the state of a single target spin, so that a collective measurement of the state of the amplifier’s spins reveals that of the target spin. Some potential implementations of these devices based on nuclear spins in naturally occurring materials will also be described.