Jeudi 19 Mai
Résumé :
Experimentally measured spectra of Josephson plasma oscillations in tunnel
junctions display signatures of coherent coupling to individual microscopic defects
acting as two-level systems (TLSs). These defects manifest themselves by
avoided level crossings in microwave spectroscopy data reflecting the dependence
of the Josephson plasma frequency on the current flowing through the
junction. They are currently understood as nanoscale dipole states emerging
from metastable lattice configurations in amorphous dielectrics forming the
tunnel barrier of the Josephson junction. Such dipolar TLSs couple to the
electrical field inside the junction which oscillates at the Josephson plasma
frequency. I will present our recent experiments in which we use a Josephson
junction for manipulating the quantum state of a single TLS. These experiments
allow to directly measure of the energy relaxation T1 and dephasing T2
times of an individual microscopic dipole-like TLS. Driving Rabi oscillations
of the junction tuned close to a resonance with TLS leads to the observation
of true 4-level dynamics. The multi-photon spectroscopy allows for direct
probing of hybridized states in the combined junction-defect coupled quantum
system. New method of direct microwave driving made it possible to study
the temperature dependence of coherence times of individual TLSs. Moreover,
the observation of TLSs which have much longer coherence times than
the macroscopic Josephson qubit renders them interesting for quantum information
processing purposes, which we experimentally explored by generating
entanglement between two TLSs mediated by the qubit.
RECRUTEMENT ACCES DIRECT
Le département de physique
Fête de la Science 2018 