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arXiv:2402.14673 · Physical Review Applied

Quasi-ideal feedback-loop supercurrent diode

Giorgio De Simoni, Francesco Giazotto

Published Jun 25, 2024• 4 citations
arXivHTMLPDF

Abstract

We suggest using a device called the bootstrap superconducting quantum interference device (BS SQUID) to break the reciprocity in charge transport. This device uses magnetic flux backaction to create a nonreciprocal current-voltage characteristic, which results in a supercurrent rectification coefficient of up to approximately 95%. The BS SQUID works as a quasi-ideal supercurrent diode (SD) and maintains its efficiency up to about 40% of its critical temperature. The external magnetic flux can be used to adjust or reverse the rectification polarity. Finally, we discuss the finite-voltage operation regime of the SD and present a possible application of our device as a half- and full-wave signal rectifier in the microwave regime.

DOI
10.1103/physrevapplied.21.064058

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We suggest using a device called the bootstrap superconducting quantum interference device (BS SQUID) to break the reciprocity in charge transport. This device uses magnetic flux backaction to create a nonreciprocal current-voltage characteristic, which results in a supercurrent rectification coefficient of up to approximately 95%. The BS SQUID works as a quasi-ideal supercurrent diode (SD) and maintains its efficiency up to about 40% of its critical temperature. The external magnetic flux can be used to adjust or reverse the rectification polarity. Finally, we discuss the finite-voltage operation regime of the SD and present a possible application of our device as a half- and full-wave signal rectifier in the microwave regime.
Abstract Back-action refers to a response that retro-acts on a system to tailor its properties with respect to an external stimulus. This self-induced effect generally belongs to both the natural and technological realm, ranging from neural networks [1] to optics [2] and electronic circuitry [3]. In electronics, back-action mechanisms are at the heart of many classes of devices such as amplifiers, oscillators, and sensors [4]. Here, we demonstrate that back-action can be successfully exploited to achieve non-reciprocal transport in superconducting circuits. Our device realizes a supercurrent diode, since the dissipationless current flows in one direction whereas dissipative transport occurs in the opposite direction. Supercurrent diodes presented so far rely on magnetic elements or vortices to mediate charge transport or external magnetic fields to break time-reversal symmetry [5-9]. In our implementation, back-action solely turns a conventional reciprocal superconducting weak link with no asymmetry between the current bias directions into a diode, where the critical current amplitude depends on the bias sign. The self-interaction of the supercurrent with the device stems from the gate tunability of the critical current, which uniquely promotes up to 88% of magnetic field-free signal rectification and diode functionality with selectable polarity. The concept we introduce is very general and can be applied directly to a large variety of devices, thereby opening novel functionalities in superconducting electronics.
It was recently experimentally proved that the superconducting counterpart of a diode, i.e., a device that realizes nonreciprocal Cooper pairs transport, can be realized by breaking the spatial and time-reversal symmetry of a system simultaneously. Here, we report the theory, fabrication, and operation of a monolithic dc superconducting quantum interference device that embedding three-dimensional Dayem nanobridges as weak links realizes an efficient and magnetic flux-tunable supercurrent diode. The device is entirely realized in Al and achieves a maximum rectification efficiency of ∼20%, which stems from the high harmonic content of its current-to-phase relation only without the need of any sizable screening current caused by a finite loop inductance. Our interferometer can be easily integrated with state-of-the-art superconducting electronics and since it does not require a finite loop inductance to provide large rectification, its downsizing is not limited by the geometrical constraints of the superconducting ring.
Diodes have a nonreciprocal voltage versus current relationship, produced by breaking the space and time reversal symmetry. However, developing high-end superconducting computers requires a superconducting analogue of the traditional semiconductor diode. Such a superconducting diode exhibits non-reciprocity, or a high asymmetry in its critical currents. We present a model of a perfect superconducting diode based on a superconducting quantum interference device made with multiple superconducting nanowires. The diode predicted by our model has a large positive critical current, while the negative critical current can be exactly zero. This 100% diode efficiency ( η = 1 ) remains stable against small changes of the magnetic field. Another important result is that under certain and quite broad conditions such devices can act as supercurrent range controllers. In such device a supercurrent can flow with zero voltage applied, but only if the supercurrent is contained in some narrow, adjustable range, which excludes zero current.
Recently, we demonstrated and analysed the superconducting quantum interference device (SQUID) bootstrap circuit (SBC). It is a direct readout scheme for dc SQUID in the voltage bias mode, permitting one to suppress the preamplifier noise. The SBC enables us to control the two key parameters of a voltage-biased SQUID: the flux-to-current transfer coefficient and the dynamic resistance. The flux-to-current, I??, characteristics of SBC are made asymmetric by introducing the additional current feedback. Depending upon the choice of the working point, this feedback can be positive (working point W2 on the steeper I?? slope) or negative (W1 on the less steep slope). The dynamic resistance is controlled by the additional voltage feedback. In our publications to date we presented only the SBC operation at W2, while in this paper we demonstrate operation at W1 and show that also in this regime the preamplifier noise suppression is possible. We used a liquid-helium-cooled Nb SQUID with a loop inductance of 350 pH and attained white flux noise of 2.5? ??0?Hz ? 1/2 both at W2 and at W1. In the latter case, the linear flux range exceeded one half-flux quantum ?0. This large linear range should lead to a significantly improved stability and slew rate of the system and also make the tolerable spread in circuit parameters much wider than in all SQUID direct readout schemes known to date. Consequently, operation in this regime opens a new path to possible SBC optimization.
Introducing new components and functionalities into quantum devices is critical in advancing state-of-the-art hardware. Here, we propose superconducting diodes (SDs) as a coherent nonreciprocal element in circuit quantum electrodynamics (cQED) architectures. In particular, we use an asymmetric SQUID as an SD controlled with a flux bias - nonreciprocal element with single control handle and on-chip modality. We spectroscopically characterize SD and show that flux bias acts cooperatively with the nonlinear diode response to induce direction-dependent resonance shifts in the transmission spectrum. We show that even with modest diode efficiency the isolation isolation ratio is sufficiently high, and scales with multiple SDs. We demonstrate the use of the SD as a coupler to realize coherent nonreciprocal qubit-qubit coupling. With a minimal two qubit system, we demonstrate nonreciprocal half-iSWAP, thereby showcasing the potential of intrinsic nonreciprocity as a tool to perform arbitrary two-qubit gates. Our work enables high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, where nonreciprocity is embedded at the device level.
Superconducting quantum interference devices (SQUIDs) that incorporate two superconductor/insulator/superconductor (SIS) Josephson junctions in a closed loop form the core of some of the most sensitive detectors of magnetic and electric fields currently available. SQUIDs in these applications are typically operated with a finite voltage which generates microwave radiation through the ac Josephson effect. This radiation may impact the system being measured. We describe here a SQUID in which the Josephson junctions are formed from strips of normal metal (N) in good electrical contact with the superconductor (S). Such SNS SQUIDs can be operated under a finite voltage bias with performance comparable or potentially better than conventional SIS SQUIDs. However, they also permit a mode of operation that is based on the unusual interplay of quasiparticle currents and supercurrents in the normal metal of the Josephson junction. The method allows measurements of the flux dependence of the critical current of the SNS SQUID without applying a finite voltage bias across the SNS junction, enabling sensitive flux detection without generating microwave radiation.