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Observing single quantum trajectories of a superconducting quantum bit

机译：观察超导量子位的单量子轨迹

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摘要

一个量子态（如一个粒子处在两个能级之间的超级位置）在与环境接触时会很快回到经典态。为了避免这种"去相干"，大部分努力通常都是将量子装置与其周围环境解耦。但也有另一种办法。Kater Murch等人发现，量子相干性能通过对环境波动的连续、准确监测来保持。他们研究了这样一个量子位：它由嵌入在一个微波腔中的一个超导装置组成，后者的波动可能会造成“去相干”。准确测量这种波动的相位或振幅的动作被发现会引导该量子位的状态沿随机轨迹变化，后者在性质上纯粹是量子性的。这项工作为在从生物系统到量子计算机的复杂环境中对量子系统进行操纵提出了一种新的控制方式，它利用的是通过测量所产生的远距离动作。%The length of time that a quantum system can exist in a superposition state is determined by how strongly it interacts with its environment. This interaction entangles the quantum state with the inherent fluctuations of the environment. If these fluctuations are not measured, the environment can be viewed as a source of noise, causing random evolution of the quantum system from an initially pure state into a statistical mixture -a process known as decoherence. However, by accurately measuring the environment in real time, the quantum system can be maintained in a pure state and its time evolution described by a 'quantum trajectory' determined by the measurement outcome. Here we use weak measurements to monitor a microwave cavity containing a superconducting quantum bit (qubit), and track the individual quantum trajectories of the system. In this setup, the environment is dominated by the fluctuations of a single electromagnetic mode of the cavity. Using a near-quantum-limited parametric amplifier, we selectively measure either the phase or the amplitude of the cavity field, and thereby confine trajectories to either the equator or a meridian of the Bloch sphere. We perform quantum state tomography at discrete times along the trajectory to verify that we have faithfully tracked the state of the quantum system as it diffuses on the surface of the Bloch sphere. Our results demonstrate that decoherence can be mitigated by environmental monitoring, and validate the foundation of quantum feedback approaches based on Bayesian statistics. Moreover, our experiments surest a new means of implementing 'quantum steering' -the harnessing of action at a distance to manipulate quantum states through measurement.
机译：一个量子态（如一个粒子处在两个能级之间的超级位置）在与环境接触时会很快回到经典态。为了避免这种"去相干"，大部分努力通常都是将量子装置与其周围环境解耦。但也有另一种办法。Kater Murch等人发现，量子相干性能通过对环境波动的连续、准确监测来保持。他们研究了这样一个量子位：它由嵌入在一个微波腔中的一个超导装置组成，后者的波动可能会造成“去相干”。准确测量这种波动的相位或振幅的动作被发现会引导该量子位的状态沿随机轨迹变化，后者在性质上纯粹是量子性的。这项工作为在从生物系统到量子计算机的复杂环境中对量子系统进行操纵提出了一种新的控制方式，它利用的是通过测量所产生的远距离动作。%The length of time that a quantum system can exist in a superposition state is determined by how strongly it interacts with its environment. This interaction entangles the quantum state with the inherent fluctuations of the environment. If these fluctuations are not measured, the environment can be viewed as a source of noise, causing random evolution of the quantum system from an initially pure state into a statistical mixture -a process known as decoherence. However, by accurately measuring the environment in real time, the quantum system can be maintained in a pure state and its time evolution described by a 'quantum trajectory' determined by the measurement outcome. Here we use weak measurements to monitor a microwave cavity containing a superconducting quantum bit (qubit), and track the individual quantum trajectories of the system. In this setup, the environment is dominated by the fluctuations of a single electromagnetic mode of the cavity. Using a near-quantum-limited parametric amplifier, we selectively measure either the phase or the amplitude of the cavity field, and thereby confine trajectories to either the equator or a meridian of the Bloch sphere. We perform quantum state tomography at discrete times along the trajectory to verify that we have faithfully tracked the state of the quantum system as it diffuses on the surface of the Bloch sphere. Our results demonstrate that decoherence can be mitigated by environmental monitoring, and validate the foundation of quantum feedback approaches based on Bayesian statistics. Moreover, our experiments surest a new means of implementing 'quantum steering' -the harnessing of action at a distance to manipulate quantum states through measurement.

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  • 来源
    《Nature》 |2013年第7470期|211-214b1|共5页
  • 作者

    K. W. Murch; S. J. Weber; C. Macklin; I. Siddiqi;

  • 作者单位

    Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA,Department of Physics, Washington University, St Louis, Missouri 63130, USA;

    Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA;

    Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA;

    Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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