37 research outputs found
The two Josephson junction flux qubit with large tunneling amplitude
In this paper we discuss solid-state nanoelectronic realizations of Josephson
flux qubits with large tunneling amplitude between the two macroscopic states.
The latter can be controlled via the height and wells form of the potential
barrier, which is determined by quantum-state engineering of the flux qubit
circuit. The simplest circuit of the flux qubit is a superconducting loop
interrupted by a Josephson nanoscale tunnel junction. The tunneling amplitude
between two macroscopically different states can be essentially increased, by
engineering of the qubit circuit, if tunnel junction is replaced by a ScS
contact. However, only Josephson tunnel junctions are particularly suitable for
large-scale integration circuits and quantum detectors with preset-day
technology. To overcome this difficulty we consider here the flux qubit with
high-level energy separation between "ground" and "excited" states, which
consists of a superconducting loop with two low-capacitance Josephson tunnel
junctions in series. We demonstrate that for real parameters of resonant
superposition between the two macroscopic states the tunneling amplitude can
reach values greater than 1K. Analytical results for the tunneling amplitude
obtained within semiclassical approximation by instanton technique show good
correlation with a numerical solution.Comment: 8 pages, 4 figure
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
The two Josephson junction flux qubit with large tunneling amplitude
In this paper we discuss solid-state nanoelectronic realizations of Josephson flux qubits with large tunneling
amplitude between the two macroscopic states. The latter can be controlled via the height and form of
the potential barrier, which is determined by quantum-state engineering of the flux qubit circuit. The simplest
circuit of the flux qubit is a superconducting loop interrupted by a Josephson nanoscale tunnel junction.
The tunneling amplitude between two macroscopically different states can be essentially increased, by
engineering of the qubit circuit, if tunnel junction is replaced by a ScS contact. However, only Josephson
tunnel junctions are particularly suitable for large-scale integration circuits and quantum detectors with preset-
day technology. To overcome this difficulty we consider here the flux qubit with high-level energy separation
between «ground» and «excited» states, which consists of a superconducting loop with two lowcapacitance
Josephson tunnel junctions in series. We demonstrate that for real parameters of resonant superposition
between the two macroscopic states the tunneling amplitude can reach values greater than 1 K. Analytical
results for the tunneling amplitude obtained within semiclassical approximation by instanton technique
show good correlation with a numerical solution
Stochastic resonance in an RF SQUID with shunted ScS junction
Using a point (superconductor–constriction–superconductor, ScS) contact in a single-Josephson-junction superconducting quantum interference device (RF SQUID) provides stochastic resonance conditions at any arbitrary small value of loop inductance and contact critical current, unlike SQUIDs with more traditional tunnel (superconductor–insulator–superconductor, SIS) junctions. This is due to the unusual potential energy of the ScS RF SQUID which always has a barrier between two wells, thus making the device bistable. This paper presents the results of a numerical simulation of the stochastic dynamics of the magnetic flux in an ScS RF SQUID loop affected by band-limited white Gaussian noise and low-frequency sine signals of small and moderate amplitudes. The difference in stochastic amplification of RF SQUID loops incorporating ScS and SIS junctions is discussed
Submicron-sized MoRe-doped Si-MoRe Josephson junctions with a low specific capacitance
Abstract We start with a short look at the problem of low-capacitance Josephson junctions, its history, and actual state-of-the-art. It is argued that such devices are important for applications requiring nonhysteretic current-voltage characteristics since reduction of capacitance by several times makes it possible to increase the device resistance by the same amount while keeping the McCumber-Stewart damping parameter unaltered. Moreover, at very high frequencies the capacitance in the RCSJ circuit with a parallel connection starts to shunt the superconducting current component due to reduction of the corresponding reactance inversely proportional to C. Hence, to extend the operating frequency range of a Josephson junction its capacitance should be as small as possible. As a solution of a new type of the Josephson device, less resistive and with smaller capacitance, we propose and realize a submicron-sized trilayer with tens nm-thick Si interlayer doped by metallic ultra-small inclusions and superconducting Mo-Re alloy electrodes