40 research outputs found
Dynamical Autler-Townes control of a phase qubit
Routers, switches, and repeaters are essential components of modern
information-processing systems. Similar devices will be needed in future
superconducting quantum computers. In this work we investigate experimentally
the time evolution of Autler-Townes splitting in a superconducting phase qubit
under the application of a control tone resonantly coupled to the second
transition. A three-level model that includes independently determined
parameters for relaxation and dephasing gives excellent agreement with the
experiment. The results demonstrate that the qubit can be used as a ON/OFF
switch with 100 ns operating time-scale for the reflection/transmission of
photons coming from an applied probe microwave tone. The ON state is realized
when the control tone is sufficiently strong to generate an Autler-Townes
doublet, suppressing the absorption of the probe tone photons and resulting in
a maximum of transmission.Comment: 8 pages, 8 figure
Coherent quantum phase slip
A hundred years after discovery of superconductivity, one fundamental
prediction of the theory, the coherent quantum phase slip (CQPS), has not been
observed. CQPS is a phenomenon exactly dual to the Josephson effect: whilst the
latter is a coherent transfer of charges between superconducting contacts, the
former is a coherent transfer of vortices or fluxes across a superconducting
wire. In contrast to previously reported observations of incoherent phase slip,
the CQPS has been only a subject of theoretical study. Its experimental
demonstration is made difficult by quasiparticle dissipation due to gapless
excitations in nanowires or in vortex cores. This difficulty might be overcome
by using certain strongly disordered superconductors in the vicinity of the
superconductor-insulator transition (SIT). Here we report the first direct
observation of the CQPS in a strongly disordered indium-oxide (InOx)
superconducting wire inserted in a loop, which is manifested by the
superposition of the quantum states with different number of fluxes. Similarly
to the Josephson effect, our observation is expected to lead to novel
applications in superconducting electronics and quantum metrology.Comment: 14 pages, 3 figure
Quantum wave mixing and visualisation of coherent and superposed photonic states in a waveguide
Superconducting quantum systems (artificial atoms) have been recently
successfully used to demonstrate on-chip effects of quantum optics with single
atoms in the microwave range. In particular, a well-known effect of four-wave
mixing could reveal a series of features beyond classical physics, when a
non-linear medium is scaled down to a single quantum scatterer. Here we
demonstrate a phenomenon of the quantum wave mixing (QWM) on a single
superconducting artificial atom. In the QWM, the spectrum of elastically
scattered radiation is a direct map of the interacting superposed and coherent
photonic states. Moreover, the artificial atom visualises photon-state
statistics, distinguishing coherent, one- and two-photon superposed states with
the finite (quantized) number of peaks in the quantum regime. Our results may
give a new insight into nonlinear quantum effects in microwave optics with
artificial atoms.Comment: 6 pages, 5 figures; accepted versio
Reducing the impact of intrinsic dissipation in a superconducting circuit by quantum error detection
A fundamental challenge for quantum information processing is reducing the impact of environmentally induced errors. Here we demonstrate a quantum error detection and rejection protocol based on the idea of quantum uncollapsing, using this protocol to reduce the impact of energy relaxation owing to the environment in a three-qubit superconducting circuit. We encode quantum information in a target qubit, and use the other two qubits to detect and reject errors caused by energy relaxation. This protocol improves the storage time of a quantum state by a factor of roughly three, at the cost of a reduced probability of success. This constitutes the first experimental demonstration of the algorithm-based improvement in the lifetime of a quantum state stored in a qubit
Non-exponential decay of a giant artificial atom
In quantum optics, light–matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions1,2. In contrast, here we experimentally demonstrate the vastly different ‘giant atom’ regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit3 to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics4. We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as non-exponential relaxation in the time domain