Decoherence in Josephson vortex quantum bits: Long-Josephson-junction approach to a two-state system

Abstract

We investigated decoherence of a Josephson vortex quantum bit ͑qubit͒ in dissipative and noisy environment. As the Josephson vortex qubit ͑JVQ͒ is fabricated by using a long Josephson junction ͑LJJ͒, we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time T 1 and on the dephasing time T . We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time T 2 is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.

Effects of a resonant cavity on macroscopic quantum tunneling of fluxons in long Josephson junctions

“…7. As earlier studies [3][4][5] indicate, MQT of fluxon between the spatially separated minima of double-well potential leads to splitting of the degenerate ground-state energy. 38,39 In this section, we estimate the effects of junction-cavity interaction on this energy splitting.…”

“…Earlier study 4 of the JVQ decoherence time by Kim, Dhungana and Park indicates that the increase in the decoherence time in noisy environment (i.e., T noise φ ) is correlated with the increasing ground-state energy splitting ∆. This suggests that, as ∆ may be tuned by adjusting the strength of junction-cavity interaction, the resonant cavity may be used to control the property of JVQ.…”

“…This observation led to much interest on Josephson vortex quantum bit [3][4][5] (qubit) as an alternative to the previously proposed superconducting qubits. Similar to other approaches based on Josephson junctions such as charge, 6 phase, 7 and flux 8 qubits, Josephson vortex qubit (JVQ) is also a promising candidate for quantum computation application.…”

“…For instance, a significantly longer decoherence time was suggested as one such advantage. 4 The JVQ takes advantage of the coherent superposition of two spatially separated states arising from the low temperture property of a trapped fluxon in a double-well potential. This property includes (i) energy quantization and (ii) macroscopic quantum tunneling 2 (MQT).…”

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

“…Recently, JJs as superconducting quantum bits [72][73][74], nanoscale superconducting quantum interference devices [75] for detecting weak flux changes, and threshold noise detectors has attracted the interest of researchers [76][77][78]. The dynamics of these devices is affected by environmental perturbations and, in particular, by random fluctuations responsible for decoherence phenomena.…”