1,230 research outputs found
A scalable architecture for quantum computation with molecular nanomagnets
A proposal for a magnetic quantum processor that consists of individual
molecular spins coupled to superconducting coplanar resonators and transmission
lines is carefully examined. We derive a simple magnetic quantum
electrodynamics Hamiltonian to describe the underlying physics. It is shown
that these hybrid devices can perform arbitrary operations on each spin qubit
and induce tunable interactions between any pair of them. The combination of
these two operations ensures that the processor can perform universal quantum
computations. The feasibility of this proposal is critically discussed using
the results of realistic calculations, based on parameters of existing devices
and molecular qubits. These results show that the proposal is feasible,
provided that molecules with sufficiently long coherence times can be developed
and accurately integrated into specific areas of the device. This architecture
has an enormous potential for scaling up quantum computation thanks to the
microscopic nature of the individual constituents, the molecules, and the
possibility of using their internal spin degrees of freedom.Comment: 27 pages, 6 figure
Experimental and numerical study of local mean age of air
This paper presents the results from the experimental and numerical study of a room with mixing ventilation, focused on the local mean age of air (LMA). The measurements were performed using the tracer gas concentration decay method. The numerical predictions were obtained from the computational fluid dynamics (CFD) module of the latest version of the ESP-r software
Multi-band quantum ratchets
We investigate directed motion in non-adiabatically rocked ratchet systems
sustaining few bands below the barrier. Upon restricting the dynamics to the
lowest M bands, the total system-plus-bath Hamiltonian is mapped onto a
discrete tight-binding model containing all the information both on the intra-
and inter-well tunneling motion. A closed form for the current in the
incoherent tunneling regime is obtained. In effective single-band ratchets, no
current rectification occurs. We apply our theory to describe rectification
effects in vortex quantum ratchets devices. Current reversals upon variation of
the ac-field amplitude or frequency are predicted.Comment: Accepted for publication in Physical Review Letter
Spectroscopy on two coupled flux qubits
We have performed spectroscopy measurements on two coupled flux qubits. The
qubits are coupled inductively, which results in a
interaction. By applying microwave radiation, we observe resonances due to
transitions from the ground state to the first two excited states. From the
position of these resonances as a function of the magnetic field applied we
observe the coupling of the qubits. The coupling strength agrees well with
calculations of the mutual inductance
Approaching Unit Visibility for Control of a Superconducting Qubit with Dispersive Readout
In a Rabi oscillation experiment with a superconducting qubit we show that a
visibility in the qubit excited state population of more than 90 % can be
attained. We perform a dispersive measurement of the qubit state by coupling
the qubit non-resonantly to a transmission line resonator and probing the
resonator transmission spectrum. The measurement process is well characterized
and quantitatively understood. The qubit coherence time is determined to be
larger than 500 ns in a measurement of Ramsey fringes.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://www.eng.yale.edu/rslab/Andreas/content/science/PubsPapers.htm
Strong magnetic coupling of an ultracold gas to a superconducting waveguide cavity
Placing an ensemble of ultracold atoms in the near field of a
superconducting coplanar waveguide resonator (CPWR) with one can
achieve strong coupling between a single microwave photon in the CPWR and a
collective hyperfine qubit state in the ensemble with kHz larger than the cavity line width of
kHz. Integrated on an atomchip such a system constitutes a hybrid quantum
device, which also can be used to interconnect solid-state and atomic qubits,
to study and control atomic motion via the microwave field, observe microwave
super-radiance, build an integrated micro maser or even cool the resonator
field via the atoms
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