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

Physics-Uspekhi

Quantum Andreev interferometer in an environment

Y. M. Galperin, L. Y. Gorelik, N. I. Lundin, Vitaly S. Shumeiko, Robert I Shekhter, M. Jonson

Published Oct 1, 2001• 3 citations
Publisher

Abstract

The influence of a noisy environment on coherent transport in Andreev states through a point contact between two superconductors is considered. The amount of dephasing is estimated for a microwave-activated quantum interferometer. Possibilities of experimentally investigating the coupling between a superconducting quantum point contact and its electromagnetic environment are discussed.

DOI
10.1070/1063-7869/44/10s/s27

Related papers

Impurity-induced dephasing of Andreev states

N. I. Lundin, Y. M. Galperin

A study is presented concerning the influence of flicker noise in the junction transparency on coherent transport in Andreev states. The amount of dephasing is estimated for a microwave-activated quantum interferometer. Possibilities of experimentally investigating the coupling between a superconducting quantum point contact and its electromagnetic environment are discussed.

arXiv:cond-mat/0003344•Physical review. B, Condensed matter•Jan 31, 2001•6 citations

Adiabatic Andreev Levels Under Irradiation - Coherent Dynamics and Dephasing

N. I. Lundin

A study of the Andreev level current through a weakly voltage-biased single-mode superconducting quantum point contact under microwave irradiation is presented. The applied microwave field induces resonant transitions between the current carrying Andreev states localized to the contact region, which results in an increase of the dc subgap current by several orders of magnitude. The applied voltage-bias couples to the superconductor phase difference across the junction, which will evolve in time. In turn the Andreev levels will oscillate adiabatically within the superconductor energy gap. Depending on the frequency of the applied field there can be either one or two resonances per oscillation period. When considering the case of two resonances the calculated dc-current exhibits an interference pattern as a function of inverse voltage. A measurement of the oscillation period would make it possible to reconstruct the Andreev level spectrum. Further, a detailed study is conducted concerning the microwave-induced current as a function of voltage bias, and the amplitude and frequency of the applied field. In realistic experimental situations there are equilibrium fluctuations of the applied voltage bias and sometimes impurity induced noise in the contact transparency. The amount of dephasing induced on the interference pattern by these fluctuations is estimated. In most cases the interference pattern will be subject to some amount of decay. However, there are parameter values for which this decay will be small. The decay originating from equilibrium fluctuations is predicted to have a non-monotonic dependence on the position of the resonances, while the decay induced by impurities should increase linearly when the separation between the resonances is increased. This difference could be used to distinguish between the two sources. The results also indicate that it should be possible to experimentally investigate the coupling between Andreev states and their environment, explicitly the impedance which the contact "sees" and the coupling strength between impurities and Andreev states.

•Jan 1, 2000•1 citation

Controlled dephasing of Andreev states in superconducting quantum point contacts

Marcelo A. Despósito, A. Levy Yeyati

We have studied the relaxation and dephasing processes in a superconducting quantum point contact induced by the interaction with an electromagnetic environment. Based on a density matrix approach we obtain the rates for the dissipative dynamics as function of the transmission, the phase difference on the contact, and the external impedance. Our calculation allows us to determine the appropriate range of parameters for the observation of coherent oscillations in the current through the contact.

arXiv:cond-mat/0108351•Physical review. B, Condensed matter•Sep 21, 2001•44 citations

Coherent processes in Superconducting quantum interferometers and qubits

J. Lantz

In this thesis we present theoretical investigations of the effects of Andreev bound states on the current transport in superconducting interferometers. We also investigate the slow dynamics of the Andreev states in a superconducting point contact, and the possible application as a quantum bit. We consider superconductor-normal metal-superconductor (SNS) and normal metalsuperconductor (NS) interferometers, where the contact region is a Y-shaped normal metal wave guide, and the two connection points to the same superconducting electrode can have different phases. The electric current in the interferometer is calculated as a function of the applied voltage and the phase difference . Andreev reflection in SNS and NS interferometers incorporates two features: interference in the arms of the Y-shaped normal region, and interplay with Andreev resonances. The latter feature yields rich phase dependent current structures in the subgap voltage region. The interference effect leads to a suppression of the current structures at . We investigate the effects on the Josephson current in NS interferometers due to current injection from the normal electrode. The two main effects of the nonequilibrium situation are: nonequilibrium population of the Andreev levels, which can result in enhancement, suppression, or even sign reversal of the Josephson current, and an anomalous interference Josephson effect, which gives rise to a long range Josephson effect, increasing with the voltage up to the superconducting gap . The two Andreev states in a superconducting quantum point contact can be accessed for manipulation and measurement by embedding the point contact in a superconducting loop. We calculate an effective Hamiltonian for the slow dynamics of the Andreev two-level system in the ring. Furthermore, we discuss methods of manipulation of the Andreev levels, and coupling of qubits. The state of the Andreev two-level system can be read out by monitoring the macroscopic quantum tunneling in a current biased Josephson junction, which is embedded in the superconducting ring of the qubit. We discuss the effects on the qubit, the readout scheme and the signal-to-noise ratio. THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Coherent processes in Superconducting quantum interferometers and qubits

•Jan 1, 2002•0 citations

Microwave sensing of Andreev bound states in a gate-defined superconducting quantum point contact

Vivek Chidambaram, Anders Kringhøj, Lucas Casparis +11 more

We use a superconducting microresonator as a cavity to sense absorption of microwaves by a superconducting quantum point contact defined by surface gates over a proximitized two-dimensional electron gas. Renormalization of the cavity frequency with phase difference across the point contact is consistent with coupling to Andreev bound states. Near \ensuremath{\pi} phase difference, we observe random fluctuations in absorption with gate voltage, related to quantum interference-induced modulations in the electron transmission. Close to pinch-off, we identify features consistent with the presence of a single Andreev bound state and describe the Andreev-cavity interaction using a Jaynes-Cummings model. By fitting the weak Andreev-cavity coupling, we extract \ensuremath{\sim}GHz decoherence consistent with charge noise and the transmission dispersion associated with a localized state.

arXiv:2102.05206•Physical Review Research•May 31, 2022•12 citations

Effects of entanglement in controlled dephasing

Alessandro Silva, Shimon Levit

In controlled dephasing a controlled environment causes dephasing of transport through a mesoscopic system. As a result of their interaction the states of the two subsystems are entangled. In this paper we discuss how their entanglement influences dephasing using as an example the ``which path detector,'' where the dephasing of transport through a quantum dot (QD) due to the interaction with a quantum point contact (QPC) is detected by means of an Aharonov-Bohm (AB) interferometer. In particular, we calculate the suppression $\ensuremath{\nu}$ of AB oscillations as a function of the bias $\mathrm{eV}$ applied to the QPC and the coupling $\ensuremath{\Gamma}$ of the QD to the leads. At low temperatures the entanglement produces a smooth crossover from $\ensuremath{\nu}\ensuremath{\propto}(eV/\ensuremath{\Gamma}{)}^{2},$ when $\mathrm{eV}\ensuremath{\ll}\ensuremath{\Gamma}$ to $\ensuremath{\nu}\ensuremath{\propto}eV/\ensuremath{\Gamma},$ for $\mathrm{eV}\ensuremath{\gg}\ensuremath{\Gamma}.$

arXiv:cond-mat/0101081•Physical review. B, Condensed matter•May 7, 2001•21 citations
The influence of a noisy environment on coherent transport in Andreev states through a point contact between two superconductors is considered. The amount of dephasing is estimated for a microwave-activated quantum interferometer. Possibilities of experimentally investigating the coupling between a superconducting quantum point contact and its electromagnetic environment are discussed.
A study of the Andreev level current through a weakly voltage-biased single-mode superconducting quantum point contact under microwave irradiation is presented. The applied microwave field induces resonant transitions between the current carrying Andreev states localized to the contact region, which results in an increase of the dc subgap current by several orders of magnitude. The applied voltage-bias couples to the superconductor phase difference across the junction, which will evolve in time. In turn the Andreev levels will oscillate adiabatically within the superconductor energy gap. Depending on the frequency of the applied field there can be either one or two resonances per oscillation period. When considering the case of two resonances the calculated dc-current exhibits an interference pattern as a function of inverse voltage. A measurement of the oscillation period would make it possible to reconstruct the Andreev level spectrum. Further, a detailed study is conducted concerning the microwave-induced current as a function of voltage bias, and the amplitude and frequency of the applied field. In realistic experimental situations there are equilibrium fluctuations of the applied voltage bias and sometimes impurity induced noise in the contact transparency. The amount of dephasing induced on the interference pattern by these fluctuations is estimated. In most cases the interference pattern will be subject to some amount of decay. However, there are parameter values for which this decay will be small. The decay originating from equilibrium fluctuations is predicted to have a non-monotonic dependence on the position of the resonances, while the decay induced by impurities should increase linearly when the separation between the resonances is increased. This difference could be used to distinguish between the two sources. The results also indicate that it should be possible to experimentally investigate the coupling between Andreev states and their environment, explicitly the impedance which the contact "sees" and the coupling strength between impurities and Andreev states.
In this thesis we present theoretical investigations of the effects of Andreev bound states on the current transport in superconducting interferometers. We also investigate the slow dynamics of the Andreev states in a superconducting point contact, and the possible application as a quantum bit. We consider superconductor-normal metal-superconductor (SNS) and normal metalsuperconductor (NS) interferometers, where the contact region is a Y-shaped normal metal wave guide, and the two connection points to the same superconducting electrode can have different phases. The electric current in the interferometer is calculated as a function of the applied voltage and the phase difference . Andreev reflection in SNS and NS interferometers incorporates two features: interference in the arms of the Y-shaped normal region, and interplay with Andreev resonances. The latter feature yields rich phase dependent current structures in the subgap voltage region. The interference effect leads to a suppression of the current structures at . We investigate the effects on the Josephson current in NS interferometers due to current injection from the normal electrode. The two main effects of the nonequilibrium situation are: nonequilibrium population of the Andreev levels, which can result in enhancement, suppression, or even sign reversal of the Josephson current, and an anomalous interference Josephson effect, which gives rise to a long range Josephson effect, increasing with the voltage up to the superconducting gap . The two Andreev states in a superconducting quantum point contact can be accessed for manipulation and measurement by embedding the point contact in a superconducting loop. We calculate an effective Hamiltonian for the slow dynamics of the Andreev two-level system in the ring. Furthermore, we discuss methods of manipulation of the Andreev levels, and coupling of qubits. The state of the Andreev two-level system can be read out by monitoring the macroscopic quantum tunneling in a current biased Josephson junction, which is embedded in the superconducting ring of the qubit. We discuss the effects on the qubit, the readout scheme and the signal-to-noise ratio. THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Coherent processes in Superconducting quantum interferometers and qubits
We use a superconducting microresonator as a cavity to sense absorption of microwaves by a superconducting quantum point contact defined by surface gates over a proximitized two-dimensional electron gas. Renormalization of the cavity frequency with phase difference across the point contact is consistent with coupling to Andreev bound states. Near \ensuremath{\pi} phase difference, we observe random fluctuations in absorption with gate voltage, related to quantum interference-induced modulations in the electron transmission. Close to pinch-off, we identify features consistent with the presence of a single Andreev bound state and describe the Andreev-cavity interaction using a Jaynes-Cummings model. By fitting the weak Andreev-cavity coupling, we extract \ensuremath{\sim}GHz decoherence consistent with charge noise and the transmission dispersion associated with a localized state.
In controlled dephasing a controlled environment causes dephasing of transport through a mesoscopic system. As a result of their interaction the states of the two subsystems are entangled. In this paper we discuss how their entanglement influences dephasing using as an example the ``which path detector,'' where the dephasing of transport through a quantum dot (QD) due to the interaction with a quantum point contact (QPC) is detected by means of an Aharonov-Bohm (AB) interferometer. In particular, we calculate the suppression $\ensuremath{\nu}$ of AB oscillations as a function of the bias eV\mathrm{eV}eV applied to the QPC and the coupling $\ensuremath{\Gamma}$ of the QD to the leads. At low temperatures the entanglement produces a smooth crossover from $\ensuremath{\nu}\ensuremath{\propto}(eV/\ensuremath{\Gamma}{)}^{2},$ when $\mathrm{eV}\ensuremath{\ll}\ensuremath{\Gamma}$ to $\ensuremath{\nu}\ensuremath{\propto}eV/\ensuremath{\Gamma},$ for $\mathrm{eV}\ensuremath{\gg}\ensuremath{\Gamma}.$