Bang–Bang Refocusing of a Qubit Exposed to Telegraph Noise
Bang–Bang Refocusing of a Qubit Exposed to Telegraph Noise
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暴露在电报噪声下的量子位的爆炸式重新聚焦
DOI：
10.1007/s11128-004-2223-0
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发表时间：
2004
影响因子：
2.5
通讯作者：
S. Lloyd
中科院分区：
文献类型：
--
作者：
H. Gutmann;F. Wilhelm;W. Kaminsky;S. Lloyd
固态量子比特具有可自然扩展到大型量子计算机体系结构的巨大优势，但它们也具有显著的缺点，即在宏观固态环境中固有地暴露于许多噪声源。通过选择适当的系统，如超导体，许多噪声源都可以被抑制。然而，纳米加工中的不精确不可避免地会导致缺陷和无序，如器件材料或衬底中的带电杂质。这种缺陷通常会产生电报噪声，因此可以建模为双稳波动。我们通过对耦合到单个双稳浮子的量子比特的详尽研究，论证了通过砰-砰控制来主动抑制这种电报噪声的可能性。我们使用随机薛定谔方程，该方程既有数值解，也有解析解。由此产生的动力学可以视作自旋矢量在布洛赫球面上的扩散。我们发现，Bang-Bang控制抑制双稳态FLuctuator的影响，其系数大致等于Bang-Bang周期与典型FLuctuator周期之比。因此，我们证明了Bang-Bang协议实质上是对此类电报噪声源的频谱进行高通滤波。这暗示了如何减少固体世界中普遍存在的1/f噪声的影响，因为它通常是由双稳涨落集合产生的。最后，我们开发了随机游走模型，该模型估计了不完美的Bang-Bang操作导致的噪声抑制水平，例如那些不能被视为δ函数脉冲的操作以及具有相位和轴误差的操作。PACS：03.65.Yz，03.67.Lx，05.40.-a
Solid state qubits promise the great advantage of being naturally scalable to large quantum computer architectures, but they also possess the significant disadvantage of being intrinsically exposed to many sources of noise in the macroscopic solid-state environment. With suitably chosen systems such as superconductors, many of sources of noise can be suppressed. However, imprecision in nanofabrication will inevitably induce defects and disorder, such as charged impurities in the device material or substrate. Such defects generically produce telegraph noise and can hence be modelled as bistable fluctuators. We demonstrate the possibility of the active suppression of such telegraph noise by bang–bang control through an exhaustive study of a qubit coupled to a single bistable fluctuator. We use a stochastic Schrödinger equation, which is solved both numerically and analytically. The resulting dynamics can be visualized as diffusion of a spin vector on the Bloch sphere. We find that bang–bang control suppresses the effect of a bistable fluctuator by a factor roughly equalling the ratio of the bang–bang period and the typical fluctuator period. Therefore, we show the bang–bang protocol works essentially as a high pass filter on the spectrum of such telegraph noise sources. This suggests how the influence of 1/f-noise ubiquitous to the solid state world could be reduced, as it is typically generated by an ensemble of bistable fluctuators. Finally, we develop random walk models that estimate the level of noise suppression resulting from imperfect bang–bang operations, such as those that cannot be treated as δ-function impulses and those that have phase and axis errors.PACS:03.65.Yz, 03.67.Lx, 05.40.-a