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Back-action supercurrent diodes

Francesco Giazotto, Daniel Margineda, Alessandro Crippa, Elia Strambini, Yuri Fukaya, Maria Teresa Mercaldo, Carmine Ortix, Mario Cuoco

Published Nov 28, 2023• 0 citations

Abstract

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.

DOI: 10.21203/rs.3.rs-3659738/v1

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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.

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.

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.

Superconducting diodes enable dissipationless directional transport, yet achieving electrical tunability and scalability remains a major challenge for circuit-level integration. Here, we demonstrate an electrothermal-switch superconducting diode in which a gate-controlled nanoscale hotspot dynamically breaks inversion symmetry in a superconducting nanowire. This mechanism gives rise to two coexisting non-reciprocal transport regimes, one associated with a non-reciprocal superconducting-to-normal transition and the other with ratchet-like vortex dynamics, both originating from the same electrothermal-switch process. The diode exhibits efficiencies up to 42 and 60% for the two regimes, respectively, and can be electrically switched on, off, or reversed in polarity in situ by applying a small gate current. These capabilities enable programmable superconducting circuits that realize electrically reconfigurable full-wave and half-wave rectification. The lithography-compatible design, high performance, and gate-controlled functionality establish a scalable platform for programmable superconducting electronics and hybrid quantum systems.

A Josephson diode is a superconducting circuit element that enables non-reciprocal transport, allowing a dissipationless supercurrent to preferentially flow in a single direction. Existing methods for achieving the required symmetry breaking mostly rely on specifically-designed materials or carefully-engineered circuits composed of multiple Josephson junctions. Here, we demonstrate that applying a biharmonic drive to a conventional superconducting tunnel-junction induces a diode effect through harmonic mixing processes that shift the supercurrent region. We show that, in a conventional tunnel junction, unity efficiency is achievable while maintaining a large supercurrent. Moreover, the relative phase between the two driving tones determines the directionality of the diode, which can be tuned in situ.

Non-reciprocal transport underpins key functionalities in signal processing and logic; however, conventional semiconductor diodes exhibit reduced performance at sub-Kelvin temperatures. As cryogenic electronics continue to scale, there is increasing demand for diode operation compatible with low-temperature and low-dissipation conditions. This need has driven the development of alternatives to p-n junctions that rely on non-reciprocal electron transport mechanisms efficient in the deep-cryogenic regime. Superconducting devices constitute a natural low-loss platform, yet most existing superconducting diodes are restricted to either Cooper-pair or quasiparticle transport, often requiring complex material stacks, asymmetric geometries, or external magnetic fields. No single, geometrically symmetric junction has yet integrated rectification across both transport channels to achieve vanishing resistance under forward bias and strongly suppressed conduction under reverse bias. Here, we demonstrate a dynamically reconfigurable dual-function superconducting diode based on a conventional Al/AlOx/Al tunnel junction. Via microwave biharmonic driving, we exploit multi-tone photon-assisted tunneling to independently control dissipationless and dissipative transport channels within the same device. Varying the microwave drive amplitude induces a transition from a supercurrent diode to an ideal quasiparticle diode, achieving rectification efficiencies exceeding those of conventional Schottky diodes and contemporary superconducting diodes. We further demonstrate AC signal rectification under both current-bias and voltage-bias configurations. Finally, we implement a proof-of-concept "absolute diode" that combines zero forward resistance with strongly suppressed reverse conduction. This tunable approach provides a versatile building block for low-power cryogenic electronic architectures.

Diode is one of the basic electronic components. It has a nonreciprocal current response, associated with a broken space/time reversal symmetry. Here we demonstrate prototypes of superconducting diodes operational at zero magnetic field. They are based on conventional niobium planar Josephson junctions, in which space/time symmetry is broken by a combination of self-field effect from nonuniform bias and stray fields from a trapped Abrikosov vortex. We demonstrate that nonreciprocity of critical current in such diodes can reach an order of magnitude and rectification efficiency can exceed 70%. Furthermore, we can easily change the diode polarity and switch nonreciprocity on/off by changing the bias configuration and by trapping/removing of a vortex. This facilitates a memory functionality. We argue that such a diode-with-memory can be used for a future generation of in-memory superconducting computers.