In a new study just published in Nature Physics Cnr Nano researchers demonstrated the possibility of exploiting the superconducting macroscopic phase to control the spectral properties of a conductor, such as its density of states; by this way it is possible to manipulate the thermal response of the conductor and hence the transport of energy. The device, defined as a thermal superconducting quantum interference proximity transistor (T-SQUIPT), has direct implications in superconducting electronics and radiation detection.
The research was entirely carried out by the Superconducting Quantum Electronics Lab (SQEL) led by Dr. Francesco Giazotto, within the NEST laboratory of Scuola Normale Superiore in Pisa and involved Nadia Ligato, Federico Paolucci and Elia Strambini. The SQEL group is investigating the development of hybrid quantum technologies where superconductors are coupled with normal metals, and in particular, in the manipulation of energy transport in mesoscopic quantum systems.
Researchers identified the superconducting macroscopic phase as the key element to perform the manipulation of the spectral properties of the metal, and therefore of the transport of energy through it, with complete phase coherence. “This result is relevant as it is the first time that the practical possibility of a coherent manipulation of the spectral properties of a metal for the purposes of thermal transport on the nanoscale has been demonstrated” says Francesco Giazotto. “Also, a remarkable consequence of this coherent manipulation lies in the demonstration of our system of having implemented the first tunable thermal memory cell with the macroscopic phase, that is, a device in which information is encoded thanks to the temperature of a metallic island”.
This study demonstrates the practical possibility of phase coherent manipulation of energy transport in quantum devices. In particular, it opens the doors to the construction of structures in which the coherent control of heat transport would allow the development of the thermal counterpart of electronic devices such as, for example, transistors and heat memories, and thermal logic gates. “From a fundamental point of view, the study effectively paves the way to the possibility of investigating chargeless modes in solid-state systems that are not accessible by conventional electronic transport, such as Majorana bound states, topological states and parafermions”, explains Giazotto. “Furthermore, the study contributes to the understanding of the energy transport and management at the nanoscale, and to the investigation of the properties of quantum thermodynamics. From the application side, this study opens the door to the creation of new-concept quantum devices such as thermal amplifiers, non-volatile memory units, and thermoelectric motors”.
Similar experimental researches in the field of heat control and energy management at the nanoscale, the so-called coherent calorithronics, have so far demonstrated the possibility of intervening on thermal currents thanks to the interference of Josephson currents present in the circuits. “This study demonstrates the possibility of altering the intrinsic spectral properties of a conductor with phase coherence, therefore it allows the manipulation of basic properties of a coherent conductor. And to do this by exploiting the superconducting macroscopic phase which is a unique peculiarity of superconducting circuits, such as our device”, concludes Giazotto.
The devices were realized at the NEST clean room using advanced nano-fabrication techniques, while the experiments were carried out at cryogenic temperatures in the quantum transport laboratories of SQEL.
Ligato, N., Paolucci, F., Strambini, E. et al. Thermal superconducting quantum interference proximity transistor. Nat. Phys. (2022). https://www.nature.com/articles/s41567-022-01578-