Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Superconductor Science and Technology

Measurement of energy relaxation time in a microwave-driven Josephson junction

Guozhu Sun, Yiwen Wang, Cao Junyu, Jian Chen, Zhengming Ji, Lin Kang, Weiwei Xu, Yang Yu, Siyuan Han

Published Oct 18, 2007• 2 citations
Publisher

Abstract

The switching current distributions P(I) with different sweep rates are obtained in microwave-driven current-biased Josephson tunnel junctions. We observe the resonant peak caused by microwave-assisted tunneling in P(I). By measuring the magnitude of the microwave resonant peak as a function of the sweep rate, we develop a novel method of extracting the energy relaxation time T1 of the junction. With this simple method, it is determined that T1 of a Nb/AlOx/Nb Josephson junction is approximately 0.5 µs.

DOI
10.1088/0953-2048/20/11/s26

Related papers

Determination of relaxation time of a Josephson junction qubit

S. K. Dutta, Haitan Xu, A. J. Berkley +5 more

When a Josephson junction in the zero-voltage state is current-biased below its critical current, the rate that it escapes to the finite-voltage state depends on the quantum state of the junction. By employing a slow current sweep, it is possible to observe experimentally the emptying of the thermally populated first excited level as a well-defined feature in the escape rate. This feature provides a simple method of determining the junction's energy relaxation time ${T}_{1}$, a key parameter for evaluating its utility for quantum computation. We discuss the temperature regime where this effect is readily observable and describe how the emptying depends directly on the relaxation time. Our model of the junction dynamics agrees well with the measured escape rate of a $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}\ifmmode\times\else\texttimes\fi{}10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ $\mathrm{Nb}\text{\ensuremath{-}}\mathrm{AlOx}\text{\ensuremath{-}}\mathrm{Nb}$ device in the 25 to $300\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ temperature range, yielding ${T}_{1}\ensuremath{\approx}4\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$.

Physical Review B•Oct 7, 2004•12 citations

Determination of Relaxation Time of a Josephson Tunnel Junction

Xueda Wen, Yang Yu

We propose a non-stationary method to measure the energy relaxation time of Josephson tunnel junctions from microwave enhanced escape phenomena. Compared with the previous methods, our method possesses simple and accurate features. Moreover, having determined the energy relaxation time, we can further obtain the coupling strength between the microwave source and the junction by changing the microwave power.

Chinese Physics Letters•Feb 1, 2008•2 citations

Time-resolved measurement of capacitance in a Josephson tunnel junction

Guozhu Sun, Jian Chen, Zhengming Ji +7 more

The capacitance of a Josephson tunnel junction is an important parameter, which determines its plasma frequency ωp and thus the energy level spacing in the quantum regime. When a microwave signal at the frequency of ω is applied to a current-biased junction in its zero-voltage state, the escape rate from this state is somehow enhanced. The enhancement is expected to go through a pronounced maximum when ωp=ω. Making use of such microwave generated resonant activation in the thermal regime, we have developed a time-resolved measurement scheme for determining the junction capacitance with an uncertainty of less than 2%.

Applied Physics Letters•Aug 21, 2006•11 citations

Dependence of Switching Current Distribution of a Current-Biased Josephson Junction on Microwave Frequency

Ji-Quan Zhai, Yongchao Li, Jianxin Shi +5 more

We investigate the distribution of the switching current of a current-biased Josephson junction (CBJJ) and its dependence on the microwave frequency using two theoretical methods, one of which is the quantum trajectory method and the other is the master equation method. Both the methods show that the distribution of the switching current of CBJJ will exhibit double peaks in a certain range of microwave frequency if proper microwave power is given, and the gap between the two peaks will increase with the microwave frequency. The obtained results can be used to identify the energy difference of the ground and first excited states in a Josephson junction for any bias current.

Chinese Physics Letters•Apr 1, 2015•3 citations

Microwave-induced phase escape in a Josephson tunnel junction

Sun Guozhu, Wang Yiwen, Cao Junyu +7 more

We perform both theoretical and experimental investigations on the phase escape of a current-biased Josephson tunnel junction under microwave irradiation. The switching current distributions exhibit abundant nonlinear behaviors depending on the power and frequency of the applied microwave. We present a model to describe the behavior of the primary peak in the switching current distribution, which is confirmed by our experimental results. The obtained features can be used to characterize the damping parameter of Josephson junctions.

Physical Review B•Mar 28, 2008•11 citations

Switching current measurements of large area Josephson tunnel junctions

Andreas J. Wallraff, Alexander V. Lukashenko, C. Coqui +3 more

We have developed a scheme for high resolution measurements of the switching current distribution of a current-biased Josephson tunnel junction using a timing technique. In the measurement setup digital control and read-out electronics are galvanically isolated from the analog sample bias electronics by an optical fiber link. We have successfully used this technique to investigate thermal activation and macroscopic quantum tunneling of the phase in a high-quality 5×5 μm2 Nb–Al/AlOx–Nb Josephson tunnel junction with a critical current of Ic≈325 μA. At temperatures above the cross over temperature of T★≈280 mK the escape is dominated by thermal activation. Due to the high quality factor of the junction (Q≈95), the escape temperature is noticeably affected by the thermal prefactor. At temperatures below T★, the value of which agrees well with the theoretical predictions, the escape of the phase by quantum mechanical tunneling is observed. The presented technique can be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing.

arXiv:cond-mat/0204527•Review of Scientific Instruments•Jul 23, 2003•74 citations
The switching current distributions P(I) with different sweep rates are obtained in microwave-driven current-biased Josephson tunnel junctions. We observe the resonant peak caused by microwave-assisted tunneling in P(I). By measuring the magnitude of the microwave resonant peak as a function of the sweep rate, we develop a novel method of extracting the energy relaxation time T1 of the junction. With this simple method, it is determined that T1 of a Nb/AlOx/Nb Josephson junction is approximately 0.5 µs.
When a Josephson junction in the zero-voltage state is current-biased below its critical current, the rate that it escapes to the finite-voltage state depends on the quantum state of the junction. By employing a slow current sweep, it is possible to observe experimentally the emptying of the thermally populated first excited level as a well-defined feature in the escape rate. This feature provides a simple method of determining the junction's energy relaxation time T1{T}_{1}T1​, a key parameter for evaluating its utility for quantum computation. We discuss the temperature regime where this effect is readily observable and describe how the emptying depends directly on the relaxation time. Our model of the junction dynamics agrees well with the measured escape rate of a $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}\ifmmode\times\else\texttimes\fi{}10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ $\mathrm{Nb}\text{\ensuremath{-}}\mathrm{AlOx}\text{\ensuremath{-}}\mathrm{Nb}$ device in the 25 to 300mK300\phantom{\rule{0.3em}{0ex}}\mathrm{mK}300mK temperature range, yielding ${T}_{1}\ensuremath{\approx}4\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$.
The capacitance of a Josephson tunnel junction is an important parameter, which determines its plasma frequency ωp and thus the energy level spacing in the quantum regime. When a microwave signal at the frequency of ω is applied to a current-biased junction in its zero-voltage state, the escape rate from this state is somehow enhanced. The enhancement is expected to go through a pronounced maximum when ωp=ω. Making use of such microwave generated resonant activation in the thermal regime, we have developed a time-resolved measurement scheme for determining the junction capacitance with an uncertainty of less than 2%.
We investigate the distribution of the switching current of a current-biased Josephson junction (CBJJ) and its dependence on the microwave frequency using two theoretical methods, one of which is the quantum trajectory method and the other is the master equation method. Both the methods show that the distribution of the switching current of CBJJ will exhibit double peaks in a certain range of microwave frequency if proper microwave power is given, and the gap between the two peaks will increase with the microwave frequency. The obtained results can be used to identify the energy difference of the ground and first excited states in a Josephson junction for any bias current.
We perform both theoretical and experimental investigations on the phase escape of a current-biased Josephson tunnel junction under microwave irradiation. The switching current distributions exhibit abundant nonlinear behaviors depending on the power and frequency of the applied microwave. We present a model to describe the behavior of the primary peak in the switching current distribution, which is confirmed by our experimental results. The obtained features can be used to characterize the damping parameter of Josephson junctions.
We have developed a scheme for high resolution measurements of the switching current distribution of a current-biased Josephson tunnel junction using a timing technique. In the measurement setup digital control and read-out electronics are galvanically isolated from the analog sample bias electronics by an optical fiber link. We have successfully used this technique to investigate thermal activation and macroscopic quantum tunneling of the phase in a high-quality 5×5 μm2 Nb–Al/AlOx–Nb Josephson tunnel junction with a critical current of Ic≈325 μA. At temperatures above the cross over temperature of T★≈280 mK the escape is dominated by thermal activation. Due to the high quality factor of the junction (Q≈95), the escape temperature is noticeably affected by the thermal prefactor. At temperatures below T★, the value of which agrees well with the theoretical predictions, the escape of the phase by quantum mechanical tunneling is observed. The presented technique can be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing.