71 research outputs found
Flux qubit as a sensor for a magnetometer with quantum limited sensitivity
We propose to use the quantum properties of a superconducting flux qubit in
the construction of a magnetometer with quantum limited sensitivity. The main
advantage of a flux qubit is that its noise is rather low, and its transfer
functions relative to the measured flux can be made to be about 10mV/,
which is an order of magnitude more than the best value for a conventional
SQUID magnetometer. We analyze here the voltage-to-flux, the phase-to-flux
transfer functions and the main noise sources. We show that the experimental
characteristics of a flux qubit, obtained in recent experiments, allow the use
of a flux qubit as magnetometer with energy resolution close to the Planck
constant.Comment: 3 pages, 6 figure
Low frequency Rabi spectroscopy for a dissipative two-level system
We have analyzed the interaction of a dissipative two level quantum system
with high and low frequency excitation. The system is continuously and
simultaneously irradiated by these two waves. If the frequency of the first
signal is close to the level separation the response of the system exhibits
undamped low frequency oscillations whose amplitude has a clear resonance at
the Rabi frequency with the width being dependent on the damping rates of the
system. The method can be useful for low frequency Rabi spectroscopy in various
physical systems which are described by a two level Hamiltonian, such as nuclei
spins in NMR, double well quantum dots, superconducting flux and charge qubits,
etc. As the examples, the application of the method to a nuclear spin and to
the readout of a flux qubit are briefly discussed.Comment: 4 pages, 3 figures, the figures are modifie
Is a single photon's wave front observable?
The ultimate goal and the theoretical limit of weak signal detection is the
ability to detect a single photon against a noisy background. [...] In this
paper we show, that a combination of a quantum metamaterial (QMM)-based sensor
matrix and quantum non-demolition (QND) readout of its quantum state allows, in
principle, to detect a single photon in several points, i.e., to observe its
wave front.
Actually, there are a few possible ways of doing this, with at least one
within the reach of current experimental techniques for the microwave range.
The ability to resolve the quantum-limited signal from a remote source against
a much stronger local noise would bring significant advantages to such diverse
fields of activity as, e.g., microwave astronomy and missile defence.
The key components of the proposed method are 1) the entangling interaction
of the incoming photon with the QMM sensor array, which produces the spatially
correlated quantum state of the latter, and 2) the QND readout of the
collective observable (e.g., total magnetic moment), which characterizes this
quantum state. The effects of local noise (e.g., fluctuations affecting the
elements of the matrix) will be suppressed relative to the signal from the
spatially coherent field of (even) a single photon.Comment: 13 pages, 4 figure
Effect of Cherenkov radiation on the jitter of solitons in the driven underdamped Frenkel-Kontorova model
The effect of complex dynamics of solitons on the output noise of the system (thermal jitter) is studied in the frame of the driven underdamped Frenkel-Kontorova model. In contrast to the continuous case, we have observed a dramatic splash of the jitter. It is demonstrated that this jitter increase is related to the joining of an initial soliton with the one generated by large amplitude oscillations of the Cherenkov radiation tail, which results in the establishment of a unified soliton structure
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