5,084 research outputs found
Resonance at the Rabi frequency in a superconducting flux qubit
We analyze a system composed of a superconducting flux qubit coupled to a
transmission-line resonator driven by two signals with frequencies close to the
resonator's harmonics. The first strong signal is used for exciting the system
to a high energetic state while a second weak signal is applied for probing
effective eigenstates of the system. In the framework of doubly dressed states
we showed the possibility of amplification and attenuation of the probe signal
by direct transitions at the Rabi frequency. We present a brief review of
theoretical and experimental works where a direct resonance at Rabi frequency
have been investigated in superconducting flux qubits. The interaction of the
qubit with photons of two harmonics has prospects to be used as a quantum
amplifier (microwave laser) or an attenuator.Comment: This paper is the extended version of the talk given by one of the
authors at the Conference On Nuclei And Mesoscopic Physics, 5-9 May 2014,
Michigan State University, East Lansing, US
Signal amplification in a qubit-resonator system
We study the dynamics of a qubit-resonator system, when the resonator is
driven by two signals. The interaction of the qubit with the high-amplitude
driving we consider in terms of the qubit dressed states. Interaction of the
dressed qubit with the second probing signal can essentially change the
amplitude of this signal. We calculate the transmission amplitude of the probe
signal through the resonator as a function of the qubit's energy and the
driving frequency detuning. The regions of increase and attenuation of the
transmitted signal are calculated and demonstrated graphically. We present the
influence of the signal parameters on the value of the amplification, and
discuss the values of the qubit-resonator system parameters for an optimal
amplification and attenuation of the weak probe signal.Comment: 7 pages, 8 figure
Distinguishing quantum from classical oscillations in a driven phase qubit
Rabi oscillations are coherent transitions in a quantum two-level system
under the influence of a resonant perturbation, with a much lower frequency
dependent on the perturbation amplitude. These serve as one of the signatures
of quantum coherent evolution in mesoscopic systems. It was shown recently [N.
Gronbech-Jensen and M. Cirillo, Phys. Rev. Lett. 95, 067001 (2005)] that in
phase qubits (current-biased Josephson junctions) this effect can be mimicked
by classical oscillations arising due to the anharmonicity of the effective
potential. Nevertheless, we find qualitative differences between the classical
and quantum effect. First, while the quantum Rabi oscillations can be produced
by the subharmonics of the resonant frequency (multiphoton processes), the
classical effect also exists when the system is excited at the overtones.
Second, the shape of the resonance is, in the classical case,
characteristically asymmetric; while quantum resonances are described by
symmetric Lorentzians. Third, the anharmonicity of the potential results in the
negative shift of the resonant frequency in the classical case, in contrast to
the positive Bloch-Siegert shift in the quantum case. We show that in the
relevant range of parameters these features allow to confidently distinguish
the bona fide Rabi oscillations from their classical Doppelganger.Comment: 8 pages, 4 figures; v2: minor corrections, Fig.1 added, introduction
expande
A METHOD FOR THE ESTIMATION OF TSUNAMI RISK ALONG RUSSIA’s FAR EAST
A simplified method was developed for estimating the tsunami risk for a coast for possible events having recurrence periods of 50 and 100 years. The method is based on readily available seismic data and the calculation of magnitudes of events with specified return periods. A classical Gumbel statistical method was used to estimate magnitudes of small probability events. The tsunami numerical modeling study used the average earthquake coordinates in the Kuril-Kamchatka high- seismic area. The verification and testing of the method were carried out using events from the North, Middle and South Kuril Islands – the most tsunami-risk areas of Russia’s Far East. Also, the study used the regional Kuril-Kamchatka catalogue of earthquakes from 1900 to 2008 - which included earthquakes with magnitudes of at least M=6. The results of the study indicate that the proposed methodology provides reasonable estimates of tsunami risk
Quantum behaviour of a flux qubit coupled to a resonator
We present a detailed theoretical analysis for a system of a superconducting
flux qubit coupled to a transmission line resonator. The master equation,
accounting incoherent processes for a weakly populated resonator, is
analytically solved. An electromagnetic wave transmission coefficient through
the system, which provides a tool for probing dressed states of the qubit, is
derived. We also consider a general case for the resonator with more than one
photon population and compare the results with an experiment on the
qubit-resonator system in the intermediate coupling regime, when the coupling
energy is comparable with the qubit relaxation rate.Comment: 16 pages, 6 figure
An approach to NLO QCD analysis of the semi-inclusive DIS data with modified Jacobi polynomial expansion method
It is proposed the modification of the Jacobi polynomial expansion method
(MJEM) which is based on the application of the truncated moments instead of
the full ones. This allows to reconstruct with a high precision the local quark
helicity distributions even for the narrow accessible for measurement Bjorken
region using as an input only four first moments extracted from the data in
NLO QCD. It is also proposed the variational (extrapolation) procedure allowing
to reconstruct the distributions outside the accessible Bjorken region
using the distributions obtained with MJEM in the accessible region. The
numerical calculations encourage one that the proposed variational
(extrapolation) procedure could be applied to estimate the full first
(especially important) quark moments
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