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Superposition of states in flux qubits with a Josephson junction of the ScS type (Review Article)
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10.1063/1.3699781
/content/aip/journal/ltp/38/4/10.1063/1.3699781
http://aip.metastore.ingenta.com/content/aip/journal/ltp/38/4/10.1063/1.3699781
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Figures

Image of FIG. 1.
FIG. 1.

The design of an RF SQUID with a pure ScS type contact: 1–Nb (99.999%) needle, 2–resonant circuit coil, 3–body, 4–Nb membrane (a). Micrograph of the membrane surface (mosaic crystal) (b). Potential U of the superconducting ring, closed by pure ScS type contact, depending on the magnetic flux Φ in the ring when external flux is Φ e  = 0.52Φ0; parameter β L  = 0.8, contact capacitance C = 3.77 fF. Magnetic flux, represented by the square of the wave function |Ψ1|2, tunnels into the right well, then the state relaxes to a lower energy level (MQT phenomenon, the process is shown by dashed lines with arrows) (c).

Image of FIG. 2.
FIG. 2.

The current-voltage characteristics VT(I0) of an RF SQUID and their derivatives dVT /dI 0(VT ) at T = 0.5 K. An RF SQUID with an oxidized ScS type contact (a). An RF SQUID with a pure ScS type contact (b). Additional peaks on the derivative of HF CVC SQUID, shown with arrows, correspond to the macroscopic resonance tunneling around degeneracy of energy levels (see Ref. 56) of a quantum oscillator.

Image of FIG. 3.
FIG. 3.

Superposition of states in a flux qubit, calculated for a three-atom point contact. The calculation was performed for parameters C = 3.77 fF, β L  = 0.8. Potential U/kB (f), expressed in units of temperature, for Φ e  = Φ0/2 with tunneling splitting of the energy levels ΔE 01/kB  = 1.52 K; the square of the wave function for the ground state is shown schematically (a). Dependences E i/kB (fe ) of the energy levels E 0, E 1, and E 2 on the external magnetic flux, expressed in units of temperature (b). Effective quantum inductance as a function of the reduced external magnetic flux (LLQ –1)eff(fe ) for different values of noise variance σ; parameter σ1/2 for curves 14 equals, respectively, 0, 0.005, 0.01, and 0.02 (c). Family of HF CVCs VT ( I 0) near low currents of excitation I 0 for Φ dc  = Φ0/2. Parameter σ1/2 for curves 13 equals, respectively, 0, 0.01, and 0.02. Curve 4 corresponds to the values Φ dc  = Φ0, σ1/2 = 0 (d).

Image of FIG. 4.
FIG. 4.

The superposition of flux qubit states, designed for a three-atom point contact of increased capacity C = 9.42 fF. Potential U/kB (f), expressed in temperature units, for Φ e  = Φ0/2 and β L  = 0.8 with a tunnel splitting ΔE 01 = 0.36 K; the square of the wave function for the ground level is shown schematically (a). Dependences E i/kB (fe ) of the energy levels E 0, E 1, and E 2 on the external magnetic flux, expressed in units of temperature (b). Effective quantum inductance as a function of the reduced external magnetic flux (LLQ –1)eff(fe ) for different values of noise variance σ; parameter σ1/2 for curves 14 equals, respectively, 0, 0.005, 0.01, and 0.02 (c). Family of HF CVCs VT (IP ) near low currents of excitation for Φ dc  = Φ0/2; parameter σ1/2 for curves 13 equals, respectively, 0, 0.01, and 0.02. Curve 4 corresponds to the values Φ dc  = Φ0, σ1/2 = 0 (d).

Image of FIG. 5.
FIG. 5.

A family of current-voltage characteristics VT (I 0) of a flux qutrit with a superposition step. The family parameter is the value of the external magnetic flux ΔΦ e ≈ Φ0 /10. The superposition step has a periodic dependence on Φ e , while the period is Φ0, and is observed around the symmetrical three-well potential. The slope of this step is partly due to the noise temperature of the resonant circuit.

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/content/aip/journal/ltp/38/4/10.1063/1.3699781
2012-04-27
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Superposition of states in flux qubits with a Josephson junction of the ScS type (Review Article)
http://aip.metastore.ingenta.com/content/aip/journal/ltp/38/4/10.1063/1.3699781
10.1063/1.3699781
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