We build on the study of single-photon heat conduction in electronic circuits taking into account the back-action of the superconductor--insulator--normal-metal thermometers. In addition, we show that placing capacitors, resistors, and superconducting quantum interference devices (SQUIDs) into a microwave cavity can severely distort the spatial current profile which, in general, should be accounted for in circuit design. The introduction of SQUIDs also allows for in situ tuning of the photonic power transfer which could be utilized in experiments on superconducting quantum bits.
We build on the study of single-photon heat conduction in electronic circuits taking into account the back-action of the superconductor--insulator--normal-metal thermometers. In addition, we show that placing capacitors, resistors, and superconducting quantum interference devices (SQUIDs) into a microwave cavity can severely distort the spatial current profile which, in general, should be accounted for in circuit design. The introduction of SQUIDs also allows for in situ tuning of the photonic power transfer which could be utilized in experiments on superconducting quantum bits.
We study photonic heat conduction between two resistors coupled weakly to a single superconducting microwave cavity. At low enough temperature, the dominant part of the heat exchanged between the resistors is transmitted by single-photon excitations of the fundamental mode of the cavity. This manifestation of single-photon heat conduction should be experimentally observable with the current state of the art. Our scheme can possibly be utilized in remote interference-free temperature control of electric components and environment engineering for superconducting quantum bits coupled to cavities.
We report our recent work on developing artificial electromagnetic environments for superconducting devices. Previously, we have showed that single-photon heat conduction between two resistors embedded in a superconducting cavity can be achieved [1]. Here, we modify this setup to provide in-situ control of the photonic heat power [2] and open up the possibility to tune the coupling strength between the artificial environment and the desired component in the cavity by several orders of magnitude. Our results provide an efficient pathway to control the lifetime of a superconducting quantum bit, qubit, allowing for rapid initialization to the ground state at will and unhindered normal operation as desired [3].
Superconducting quantum bits are one of the leading frontrunners in the race to build a solid-state quantum computer. In circuit quantum electrodynamics (cQED), electronic quantum circuits, playing the role of quantum bits, qubits, are placed into superconducting cavities with incredibly weak dissipation. The resulting system exhibits both photon and qubit characteristics, and it is possible to perform complex operations by driving the system with microwaves. Progress has been rapid, with vast improvements in cavities, qubits, and in controlling the interaction between the two. As a result, the first simple quantum algorithms to utilize this architecture have recently been implemented. \nAt the same time, there have been significant developments in improving our understanding of the heat flow in nanoelectronics. In particular the development of tunnel junctions has reached such a level, that it is now possible to control and measure the temperature of small metal islands with high precision. Such techniques have enabled the first observations of quantum-limited heat conduction through the photonic modes of a circuit. \nThis thesis introduces some of the benefits that come with the unification of these two fields. Theoretical models for experiments in a superconducting cavity are presented, with heat conduction due to individual cavity photons discussed in detail, along with a novel method to vary the lifetime of a qubit over many orders of magnitude. The realisation of these experiments would be the first steps on the road to integrating normal-metal components with cQED.
Circuit quantum electrodynamics offers versatile opportunities for various discoveries infundamental physics, as well as for different applications such as sensitive detectors and,ultimately, even a large-scale quantum computer. Since these devices work at cryogenictemperatures and excess heat is a substantial source of errors, it is of great importance to controlthe heat.
In this thesis, several techniques for heat control are experimentally investigated. We study heattransfer carried by photons between two heat baths, as well as heat flow between superconductingresonators and their environment. In particular, the focus is on using normal-metal componentsto enhance the operation of superconducting microwave circuits operating at the level of singleenergy quanta.
First, we investigate long-distance single-channel heat conduction near the quantum limit, i.e.,the quantum of thermal conductance. As compared to earlier experiments, the distance is increasedby a factor of 10,000. In addition, we demonstrate emission and absorption of photons in amicrowave resonator by photon-assisted tunneling in normal-metal–insulator–superconductorjunctions. Another approach for absorbing photons is to use a normal-metal resistor in asuperconducting resonator with a tunable resonance frequency. Finally, we realize a circuitconsisting of two resonators with a singularity in the parameter space, known as an exceptionalpoint. In our circuit, the exceptional point enables the fastest possible heat transfer between thetwo resonators without back and forth oscillation.
In the future, these methods may find applications in different cryogenic devices, including a fastinitialization of qubits. Furthermore, the methods may be utilized in the experimental studies offundamental physics, including further investigations of exceptional points in differentconfigurations.; Piirikvanttisahkodynamiikka tarjoaa monipuolisia mahdollisuuksia seka monenlaisilleperusfysiikkaan liittyville havainnoille etta erilaisille sovelluksille, kuten herkille ilmaisimille jalopulta jopa suuren mittakaavan kvanttitietokoneelle. Lammonsaately on erityisen tarkeaa, sillatallaiset laitteet toimivat erittain matalissa lampotiloissa ja ylimaarainen lampo aiheuttaamerkittavissa maarin toimintavirheita.
Vaitoskirjassa tutkitaan kokeellisesti useita menetelmia lammonsaatelyyn. Tutkimuskohteena onsateilyhiukkasten eli fotonien lammonkuljetus kahden lampokylvyn valilla seka suprajohtavienvarahtelijoiden lammonsiirto ymparistonsa kanssa. Erityisesti tutkitaan normaalimetallistavalmistettujen osien kayttoa suprajohtavissa mikroaaltopiireissa, jotka toimivat yksittaistenenergiakvanttien tasolla ja joiden toimintaa normaalimetalliosilla pyritaan parantamaan.
Aluksi vaitoskirjassa tutkitaan pitkilla etaisyyksilla yksittaista kanavaa pitkin tapahtuvaalammonsiirtoa kvanttimekaniikan maaraamalla rajalla, joka on ns. lammonjohtavuuskvantti.Aikaisempiin tutkimuksiin verrattuna etaisyytta on kasvatettu tekijalla 10 000. Lisaksivaitoskirjassa osoitetaan fotonien kaappaus eli…
Circuit quantum electrodynamics offers versatile opportunities for various discoveries infundamental physics, as well as for different applications such as sensitive detectors and,ultimately, even a large-scale quantum computer. Since these devices work at cryogenictemperatures and excess heat is a substantial source of errors, it is of great importance to controlthe heat. In this thesis, several techniques for heat control are experimentally investigated. We study heattransfer carried by photons between two heat baths, as well as heat flow between superconductingresonators and their environment. In particular, the focus is on using normal-metal componentsto enhance the operation of superconducting microwave circuits operating at the level of singleenergy quanta. First, we investigate long-distance single-channel heat conduction near the quantum limit, i.e.,the quantum of thermal conductance. As compared to earlier experiments, the distance is increasedby a factor of 10,000. In addition, we demonstrate emission and absorption of photons in amicrowave resonator by photon-assisted tunneling in normal-metal–insulator–superconductorjunctions. Another approach for absorbing photons is to use a normal-metal resistor in asuperconducting resonator with a tunable resonance frequency. Finally, we realize a circuitconsisting of two resonators with a singularity in the parameter space, known as an exceptionalpoint. In our circuit, the exceptional point enables the fastest possible heat transfer between thetwo resonators without back and forth oscillation. In the future, these methods may find applications in different cryogenic devices, including a fastinitialization of qubits. Furthermore, the methods may be utilized in the experimental studies offundamental physics, including further investigations of exceptional points in differentconfigurations.
We investigate the photon-mediated thermal transport between a superconducting electrode and a normal metal. When the quasiparticle contribution can be neglected, the photon-mediated channel becomes an efficient heat transport relaxation process for the superconductor at low temperatures, being larger than the intrinsic contribution due to the electron–phonon interaction. Furthermore, the superconductor–normal metal system acts as a nearly perfect thermal diode, with a rectification factor up to 108 for a realistic aluminum superconductor. The rectification factor can also be tuned in a phase-controlled fashion through a non-galvanic coupling, realized by changing the magnetic flux piercing a superconducting quantum interference device, which modifies the coupling impedance between the superconductor and the normal metal. The scheme can be exploited for passive cooling in superconducting quantum circuits by transferring heat toward normal metallic pads where it dissipates more efficiently or for more general thermal management purposes.