Frequency spectrum of a superconducting metadevice (original) (raw)
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Modulated microwave absorption of a superconducting loop with two nonidentical Josephson junctions
Physical Review B, 1991
A regularly spaced multiline modulated-microwave-absorption (MMA) spectrum arising from two lead pieces behaving as a quantum interferometer is modeled by replacing the microwave current across two parallel Josephson junctions by a direct current I that is proportional to the square root of the microwave power P. Assuming that microwave absorption occurs only when I is greater than the field-dependent critical current I, of the two-junction system, the peak-to-peak width 6H of each MMA line is shown to depend on P according to the relation P =Pa+(1-cos6n), where 6n=~6H/AH, and AH is the separation of neighboring lines. The experimental data previously obtained by Drumheller, Trybula, and Stankowski were fitted to the values Po =3 mW and a=66 mW, which leads to a ratio I, /Ib of 1.4 for the critical currents of the two junctions. A surprisingly good fit of the data to the more approximate relation P =Po+ b (6H) is obtained for the values Po =3 mW and b=74 mW/Oe. Predictions of the above model are compared with those of the recent theory of Vichery, Beuneu, and Lejay.
Journal of Applied Physics, 2000
We measured the amplitude-frequency characteristics of radio frequency superconducting quantum interference devices ͑rf SQUIDs͒ over a temperature range between 65 and 79 K. Using the expressions derived from the recently developed rf SQUID theory, valid also at large thermal fluctuations, we determined from these data the basic parameters of high-transition-temperature superconductor ͑HTS͒ rf SQUIDs. These parameters were: ͑a͒ the high-frequency coupling coefficient between the rf SQUID and the tank circuit resonator, k, ͑b͒ the SQUIDs hysteretic parameter, , ͑c͒ the critical current of the Josephson junction, I c , ͑d͒ its normal resistance, R n , and ͑e͒ its noise parameter, ⌫. We found a good agreement with the values of (I c) and R n determined directly after destructively opening the SQUID loop. In accordance with the theoretical predictions, our experimental results show that at large thermal fluctuation levels (TХ77 K), rf SQUIDs with large loop inductance operate in nonhysteretic mode up to  values exceeding 3. Furthermore, we have shown that the optimal energy sensitivity is attained in the nonhysteretic mode at a value of  distinctly higher than 1. A quantitative comparison of white noise predicted by the theory with that obtained from the experiment showed a reasonable agreement. We also discussed the contribution of the phase information to the SQUID's signal and noise at optimum operation conditions, when a mixer was used as a signal detector.
Macroscopic quantum behavior of superconducting quantum interference devices
Fortschritte der Physik, 2003
Superconducting quantum interference devices (SQUIDs) are made by a superconducting loop interrupted by one or more Josephson junctions. They are described in terms of a macroscopic variable, the magnetic flux, which shows quantum effects such as tunnelling through a potential barrier. Besides making up the source of a quantum state, SQUIDs also provide the instruments necessary for its probing: as a fact, SQUID based magnetometers have a sensitivity approaching the quantum limit. In this paper I will review the working principle of these devices and illustrate the system of SQUIDs realized in my group to test the quantum behavior at a macroscopic level. *
Chapter 3 . Superconducting and Quantum-Effect Electronics
2009
Arrays of junctions provide for relatively large power but due to nonlinearities they can exhibit diverse complex spatiotemporal patterns. Experiments, simulations and analysis were performed on a broad range of discrete arrays of Josephson-junction oscillators in order to understand their ability to produce coherent radiation. Networks ranging from single square and triangular plaquettes to oneand twodimensional arrays are studied. In each array, the junctions are identical and underdamped, and the arrays are driven by dc bias currents. Although few analytical results are known for these systems, we study the technically interesting solutions which can be represented as traveling waves. It is in this mode that the devices can be used as submillimeter wave sources.
Radio-frequency method for investigation of quantum properties of superconducting structures
Low Temperature Physics, 2004
We implement the impedance measurement technique (IMT) for characterization of interferometer-type superconducting qubits. In the framework of this method, the interferometer loop is inductively coupled to a high-quality tank circuit. We show that the IMT is a powerful tool to study a response of externally controlled two-level system to different types of excitations. Conclusive information about qubits is obtained from the read-out of the tank properties.
Interference effect heat conductance in a Josephson junction and its detection in an rf SQUID
Physical Review B, 1998
The energy current through a superconductor-insulator-superconductor Josephson junction consists of a quasiparticle current, an interference current, and a pair current. The quasiparticle part represents the normal dissipative heat current. This part is shown to have a unique temperature dependence. The other two parts depend on the phase drop across the junction. When the junction is biased by a fixed temperature drop, the interference current can flow in either direction, depending on the sign of cos. This gives rise to an effect in which the total heat current oscillates with the phase drop across the junction. We suggest an experimental setup involving an rf superconducting quantum interference device, which is designed to measure these effects.
Quantum State Engineering With the Rf-SQUID: A Brief Introduction
Arxiv preprint quant-ph/0307101, 2003
The SQUID, or superconducting quantum interference device, is a highly sensitive instrument employed for the nondestructive measurement of magnetic fields, with a host of applications in both biophysics and materials technology. It is composed of a cooled superconductive metal ring separated by a thin insulating barrier of non-superconducting metal. Electrons tunnel across the barrier to form a Josephson junction; an rf SQUID is essentially a Josephson junction with tunable current and energy. Quantum computers take advantage of the superpositional logic of quantum mechanics to allow for dramatic increases in computational efficiency. rf SQUIDs show potential for quantum computing applications by forming the qubit component of a quantum computer, through simply treating the direction of current, clockwise or counterclockwise, as the value of the bit.
Coherent oscillations in a superconducting tunable flux qubit manipulated without microwaves
New Journal of Physics, 2009
We experimentally demonstrate the coherent oscillations of a tunable superconducting flux qubit by manipulating its energy potential with a nanosecond-long pulse of magnetic flux. The occupation probabilities of two persistent current states oscillate at a frequency ranging from 6 GHz to 21 GHz, tunable via the amplitude of the flux pulse. The demonstrated operation mode allows to realize quantum gates which take less than 100 ps time and are thus much faster compared to other superconducting qubits. An other advantage of this type of qubit is its insensitivity to both thermal and magnetic field fluctuations.
Physical review, 2022
Strong nonlinearity of a self-resonant radio frequency superconducting quantum interference device (rf-SQUID) meta-atom is explored via intermodulation (IM) measurements. Previous work in zero dc magnetic flux showed a sharp onset of IM response as the frequency sweeps through the resonance. A second onset at higher frequency was also observed, creating a prominent gap in the IM response. By extending those measurements to nonzero dc flux, new dynamics are revealed, including: dc flux tunabililty of the aforementioned gaps, and enhanced IM response near geometric resonance of the rf-SQUID. These features observed experimentally are understood and analyzed theoretically through a combination of a steady state analytical modeling, and a full numerical treatment of the rf SQUID dynamics. The latter, in addition, predicts the presence of chaos in narrow parameter regimes. The understanding of intermodulation in rf-SQUID metamaterials is important for producing low-noise amplification of microwave signals and tunable filters.
Physical Review B, 2013
In this work we show that a tunable coupling between microwave resonators can be engineered by means of simple Josephson junctions circuits, such as dc-and rf-SQUIDs. We show that by controlling the time dependence of the coupling it is possible to switch on and off and modulate the cross-talk, boost the interaction towards the ultrastrong regime, as well as to engineer red and blue sideband couplings, nonlinear photon hopping and classical gauge fields. We discuss how these dynamically tunable superconducting circuits enable key applications in the fields of all optical quantum computing, continuous variable quantum information and quantum simulation-all within the reach of state of the art in circuit-QED experiments.