1,811 research outputs found
Cavity QED with separate photon storage and qubit readout modes
We present the realization of a cavity quantum electrodynamics setup in which
photons of strongly different lifetimes are engineered in different harmonic
modes of the same cavity. We achieve this in a superconducting transmission
line resonator with superconducting qubits coupled to the different modes. One
cavity mode is strongly coupled to a detection line for qubit state readout,
while a second long lifetime mode is used for photon storage and coherent
quantum operations. We demonstrate sideband based measurement of photon
coherence, generation of n photon Fock states and the scaling of the sideband
Rabi frequency with the square root of n using a scheme that may be extended to
realize sideband based two-qubit logic gates.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Characterization of a microwave frequency resonator via a nearby quantum dot
We present measurements of a hybrid system consisting of a microwave
transmission-line resonator and a lateral quantum dot defined on a GaAs
heterostructure. The two subsystems are separately characterized and their
interaction is studied by monitoring the electrical conductance through the
quantum dot. The presence of a strong microwave field in the resonator is found
to reduce the resonant conductance through the quantum dot, and is attributed
to electron heating and modulation of the dot potential. We use this
interaction to demonstrate a measurement of the resonator transmission spectrum
using the quantum dot.Comment: 3 pages, 3 figure
Using Sideband Transitions for Two-Qubit Operations in Superconducting Circuits
We demonstrate time resolved driving of two-photon blue sideband transitions
between superconducting qubits and a transmission line resonator. Using the
sidebands, we implement a pulse sequence that first entangles one qubit with
the resonator, and subsequently distributes the entanglement between two
qubits. We show generation of 75% fidelity Bell states by this method. The full
density matrix of the two qubit system is extracted using joint measurement and
quantum state tomography, and shows close agreement with numerical simulation.
The scheme is potentially extendable to a scalable universal gate for quantum
computation.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Simultaneous bistability of qubit and resonator in circuit quantum electrodynamics
We explore the joint activated dynamics exhibited by two quantum degrees of
freedom: a cavity mode oscillator which is strongly coupled to a
superconducting qubit in the strongly coherently driven dispersive regime.
Dynamical simulations and complementary measurements show a range of parameters
where both the cavity and the qubit exhibit sudden simultaneous switching
between two metastable states. This manifests in ensemble averaged amplitudes
of both the cavity and qubit exhibiting a partial coherent cancellation.
Transmission measurements of driven microwave cavities coupled to transmon
qubits show detailed features which agree with the theory in the regime of
simultaneous switching
Thermal Excitation of Multi-Photon Dressed States in Circuit Quantum Electrodynamics
The exceptionally strong coupling realizable between superconducting qubits
and photons stored in an on-chip microwave resonator allows for the detailed
study of matter-light interactions in the realm of circuit quantum
electrodynamics (QED). Here we investigate the resonant interaction between a
single transmon-type multilevel artificial atom and weak thermal and coherent
fields. We explore up to three photon dressed states of the coupled system in a
linear response heterodyne transmission measurement. The results are in good
quantitative agreement with a generalized Jaynes-Cummings model. Our data
indicates that the role of thermal fields in resonant cavity QED can be studied
in detail using superconducting circuits.Comment: ArXiv version of manuscript to be published in the Physica Scripta
topical issue on the Nobel Symposium 141: Qubits for Future Quantum
Computers(2009), 13 pages, 6 figures, hi-res version at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Double-sided coaxial circuit QED with out-of-plane wiring
Superconducting circuits are well established as a strong candidate platform
for the development of quantum computing. In order to advance to a practically
useful level, architectures are needed which combine arrays of many qubits with
selective qubit control and readout, without compromising on coherence. Here we
present a coaxial circuit QED architecture in which qubit and resonator are
fabricated on opposing sides of a single chip, and control and readout wiring
are provided by coaxial wiring running perpendicular to the chip plane. We
present characterisation measurements of a fabricated device in good agreement
with simulated parameters and demonstrating energy relaxation and dephasing
times of s and s respectively. The architecture
allows for scaling to large arrays of selectively controlled and measured
qubits with the advantage of all wiring being out of the plane.Comment: 4 pages, 3 figures, 1 tabl
Dynamics of dispersive single qubit read-out in circuit quantum electrodynamics
The quantum state of a superconducting qubit nonresonantly coupled to a
transmission line resonator can be determined by measuring the quadrature
amplitudes of an electromagnetic field transmitted through the resonator. We
present experiments in which we analyze in detail the dynamics of the
transmitted field as a function of the measurement frequency for both weak
continuous and pulsed measurements. We find excellent agreement between our
data and calculations based on a set of Bloch-type differential equations for
the cavity field derived from the dispersive Jaynes-Cummings Hamiltonian
including dissipation. We show that the measured system response can be used to
construct a measurement operator from which the qubit population can be
inferred accurately. Such a measurement operator can be used in tomographic
methods to reconstruct single and multiqubit states in ensemble-averaged
measurements.Comment: Revised version: corrected typos, 8 pages, 6 figures, version with
high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Quantum-to-Classical Transition in Cavity Quantum Electrodynamics
The quantum properties of electromagnetic, mechanical or other harmonic
oscillators can be revealed by investigating their strong coherent coupling to
a single quantum two level system in an approach known as cavity quantum
electrodynamics (QED). At temperatures much lower than the characteristic
energy level spacing the observation of vacuum Rabi oscillations or mode
splittings with one or a few quanta asserts the quantum nature of the
oscillator. Here, we study how the classical response of a cavity QED system
emerges from the quantum one when its thermal occupation -- or effective
temperature -- is raised gradually over 5 orders of magnitude. In this way we
explore in detail the continuous quantum-to-classical crossover and demonstrate
how to extract effective cavity field temperatures from both spectroscopic and
time-resolved vacuum Rabi measurements.Comment: revised version: improved analysis, 4 pages, 4 figures, hi-res
version available at http://qudev.ethz.ch/content/science/PubsPapers.htm
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