Towards phase-coherent caloritronics in superconducting circuits

Abstract

The emerging field of phase-coherent caloritronics (from the Latin word "calor", i.e., heat) is based on the possibility to control heat currents using the phase difference of the superconducting order parameter. The goal is to design and implement thermal devices able to master energy transfer with a degree of accuracy approaching the one reached for charge transport by contemporary electronic components. This can be obtained by exploiting the macroscopic quantum coherence intrinsic to superconducting condensates, which manifests itself through the Josephson and the proximity effect. Here, we review recent experimental results obtained in the realization of heat interferometers and thermal rectifiers, and discuss a few proposals for exotic non-linear phase-coherent caloritronic devices, such as thermal transistors, solid-state memories, phase-coherent heat splitters, microwave refrigerators, thermal engines and heat valves. Besides being very attractive from the fundamental physics point of view, these systems are expected to have a vast impact on many cryogenic microcircuits requiring energy management, and possibly lay the first stone for the foundation of electronic thermal logic.In the last decades, the impressive evolution of modern electronics has reached a point where quantum effects and phase coherence are ordinarily exploited to study exotic phenomena at the nanoscale under controlled and adjustable conditions. Only very recently, instead, scientists have started to exploit the great potentialities offered by nanotechnology for the investigation and control of heat currents (the branch of science called "caloritronics"). Interesting advances in the understanding of fundamental properties of thermal transport have been obtained in experiments involving atomic or molecular junctions [1]. A few works [2][3][4] have shown that heat flow has a quantum limit -just as the electric current -and that this limit does not depend on the nature of heat carriers. Furthermore, a remarkable amount of theoretical and experimental studies has been focused on the interaction between heat and spin currents in thermoelectric devices [5].From the point of view of applications, the largest effort has been put into electronic and phononic thermometry or refrigeration [6][7][8], but the most intriguing and ambitious goal has always been the full control of heat currents, aiming to emulate the accuracy regularly obtained for charge transport in modern electronic devices. This attracting possibility was first envisioned by a conspicuous amount of theoretical works designing non-linear phononic devices [9]. However, the practical realization of these structures still appears challenging, hampering significant improvements of the first promising results [10,11]. An appealing alternative is represented by the notable ingredient of phase coherence, whose role in thermal transport was almost unknown until ten years ago, with just the exceptions of Refs. 12-14. This gap was filled by the birth of phase-coherent caloritronics [3,15,16]...

Hysteretic Superconducting Heat-Flux Quantum Modulator

“…Before exploring the behavior of the total heat current by changing the temperatures T 1 and T 2 of the electrodes, we observe that the hysteretic parameter β depends on them through the critical current I a J according to Eq. (9). As is clearly shown in Fig.…”

“…Recently, the features of the phase-coherent thermal transport in Josephson devices have been investigated and confirmed experimentally in several interferometer-like structures [2][3][4][5][6][7][8][9]. In Ref.…”

InAs nanowire superconducting tunnel junctions: Quasiparticle spectroscopy, thermometry, and nanorefrigeration

“…A peak refrigeration of about δT = 10 mK is achieved at a bath temperature T bath ≈ 250 − 350 mK in our prototype devices. This method opens important perspectives for the investigation of thermoelectric effects in semiconductor nanostructures and for nanoscale refrigeration.The control over the heat flow and the local electron distribution in a nanodevice represents a crucial experimental challenge [1][2][3] with an important impact both on the solution of key open problems in fundamental physics and on development of future device applications [4,5]. In particular, the recent progress of thermoelectric physics in nanostructured materials offers fascinating new perspectives for the realization of more efficient solid-state heat pumps for energy conversion [6][7][8] and/or for the creation of self-cooling nanodevices where the electron or the phonon system in the active region can be refrigerated below the phonon bath [3,4].…”

“…Local electronic cooling can be relevant for improving the device performance either in terms of noise, sensitivity or decoherence [4] and for finding a role in advanced applications, including topological quantum computation [13][14][15][16] and ultrasensitive radiation detection [17,18]. In addition, the manipulation of heat is at the basis of the emerging field of coherent caloritronics [1,[19][20][21] and it could be crucial in solving important standing fundamental problems in condensed matter physics, including quantum thermodynamics and the study of the elusive Majorana fermions in solid-state systems [13,22,23].Hybrid architectures combining superconductive elements with normal metals represent a bright example of refined technology to locally measure and manipulate heat at low temperatures and have been the subject of an intense research effort [3][4][5]. In particular, devices integrating normal-insulator-superconductor (NIS) tunnel junctions between a normal metal (N) and Al [24] or other superconductors (S) [25,26] have yielded the demonstration of significant nanorefrigeration in the milliKelvin regime.…”

“…Hybrid architectures combining superconductive elements with normal metals represent a bright example of refined technology to locally measure and manipulate heat at low temperatures and have been the subject of an intense research effort [3][4][5]. In particular, devices integrating normal-insulator-superconductor (NIS) tunnel junctions between a normal metal (N) and Al [24] or other superconductors (S) [25,26] have yielded the demonstration of significant nanorefrigeration in the milliKelvin regime.…”