Abstract
We discuss the noise occurring during a classical dissipative switching process as it would be detected by a quantum bit used as a detector for noise. In particular we study the switching-induced decoherence during escape events. We present a simple method to obtain analytical results for the qubit dephasing and bit-flip, which goes beyond the simple Born-Markov notion of the qubit as a spectrometer for noise but still allows us to correlate its behavior with the noise source. These results also provide insight into the qubit measurement process involving a switching type of detector, showing under which conditions switching detectors can be operated fast and with low error. In particular, the state in the end recovers from temporary bit flip errors due to an intrinsic approximate time reversal symmetry, whereas the switching process mostly produces low frequency pure dephasing noise.
Highlights
1 Introduction Noise-activated switching out of a metastable state is a common phenomenon in a wide range of physical systems, including Josephson junctions, nanomechanical devices, and chemical reactions [, ]
Examples of switching detectors include the superconducting quantum interference device (SQUID) [ – ], where switching occurs between the superconducting and dissipative state and is driven by quantum fluctuations, and the Josephson bifurcation amplifier (JBA) [ – ], which has been employed in the delicate task of detecting a qubit state in a minimally invasive fashion [ ]
The detector can switch between different, weakly dissipative, dynamical states based on quantum activation [ ] or dynamical tunneling [ ]
Summary
Noise-activated switching out of a metastable state is a common phenomenon in a wide range of physical systems, including Josephson junctions, nanomechanical devices, and chemical reactions [ , ]. Examples of switching detectors include the superconducting quantum interference device (SQUID) [ – ], where switching occurs between the superconducting and dissipative state and is driven by quantum fluctuations, and the Josephson bifurcation amplifier (JBA) [ – ], which has been employed in the delicate task of detecting a qubit state in a minimally invasive fashion [ ]. In this case, the detector can switch between different, weakly dissipative, dynamical states based on quantum activation [ ] or dynamical tunneling [ ]. Switching detectors are currently receiving renewed attention for their potential as microwave photon counters [ – ]
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