92 research outputs found
Geometric phases in superconducting qubits beyond the two-level-approximation
Geometric phases, which accompany the evolution of a quantum system and
depend only on its trajectory in state space, are commonly studied in two-level
systems. Here, however, we study the adiabatic geometric phase in a weakly
anharmonic and strongly driven multi-level system, realised as a
superconducting transmon-type circuit. We measure the contribution of the
second excited state to the two-level geometric phase and find good agreement
with theory treating higher energy levels perturbatively. By changing the
evolution time, we confirm the independence of the geometric phase of time and
explore the validity of the adiabatic approximation at the transition to the
non-adiabatic regime.Comment: 5 pages, 3 figure
Electromagnetically induced transparency on a single artificial atom
We present experimental observation of electromagnetically induced
transparency (EIT) on a single macroscopic artificial "atom" (superconducting
quantum system) coupled to open 1D space of a transmission line. Unlike in a
optical media with many atoms, the single atom EIT in 1D space is revealed in
suppression of reflection of electromagnetic waves, rather than absorption. The
observed almost 100 % modulation of the reflection and transmission of
propagating microwaves demonstrates full controllability of individual
artificial atoms and a possibility to manipulate the atomic states. The system
can be used as a switchable mirror of microwaves and opens a good perspective
for its applications in photonic quantum information processing and other
fields
Geometric Phase and Non-Adiabatic Effects in an Electronic Harmonic Oscillator
Steering a quantum harmonic oscillator state along cyclic trajectories leads
to a path-dependent geometric phase. Here we describe an experiment observing
this geometric phase in an electronic harmonic oscillator. We use a
superconducting qubit as a non-linear probe of the phase, otherwise
unobservable due to the linearity of the oscillator. Our results demonstrate
that the geometric phase is, for a variety of cyclic trajectories, proportional
to the area enclosed in the quadrature plane. At the transition to the
non-adiabatic regime, we study corrections to the phase and dephasing of the
qubit caused by qubit-resonator entanglement. The demonstrated controllability
makes our system a versatile tool to study adiabatic and non-adiabatic
geometric phases in open quantum systems and to investigate the potential of
geometric gates for quantum information processing
Microwave-controlled generation of shaped single photons in circuit quantum electrodynamics
Large-scale quantum information processors or quantum communication networks
will require reliable exchange of information between spatially separated
nodes. The links connecting these nodes can be established using traveling
photons that need to be absorbed at the receiving node with high efficiency.
This is achievable by shaping the temporal profile of the photons and absorbing
them at the receiver by time reversing the emission process. Here, we
demonstrate a scheme for creating shaped microwave photons using a
superconducting transmon-type three-level system coupled to a transmission line
resonator. In a second-order process induced by a modulated microwave drive, we
controllably transfer a single excitation from the third level of the transmon
to the resonator and shape the emitted photon. We reconstruct the density
matrices of the created single-photon states and show that the photons are
antibunched. We also create multipeaked photons with a controlled amplitude and
phase. In contrast to similar existing schemes, the one we present here is
based solely on microwave drives, enabling operation with fixed frequency
transmons
Dynamics of coherent and incoherent emission from an artificial atom in a 1D space
We study dynamics of an artificial two-level atom in an open 1D space by
measuring evolution of its coherent and incoherent emission. States of the atom
-- a superconducting flux qubit coupled to a transmission line -- are fully
controlled by resonant excitation microwave pulses. The coherent emission -- a
direct measure of superposition in the atom -- exhibits decaying oscillations
shifted by from oscillations of the incoherent emission, which, in
turn, is proportional to the atomic population. The emission dynamics provides
information about states and properties of the atom. By measuring the coherent
dynamics, we derive two-time correlation function of fluctuations and, using
quantum regression formula, reconstruct the incoherent spectrum of the
resonance fluorescence triplet, which is in a good agreement with the directly
measured one.Comment: 4 pages, 4 figure
- …