By longitudinal combination of two superconducting resonators, we realise a superconducting circulus analogue to the generic Hamilton cavity-optomechanical, which are of a different order of dimension. Longitudinal connections are achieved by incorporating a superconducting quantum interference into a high frequency resonator, so that the frequency of its resonance depends upon the zero-point current fluctuations of the nearby low frequency LC resonator. By using sideband drive fields the intrinsic coupling power is increased by controlling the amplitude of the drive field by around 15 kHz to 280 kHz. Our findings pave the way for the examination in a completely superconducting platform of optomechanical effects and allow quantum optical experiments with radiofrequencybands in which photons are unexplored. We consider a design for a cyclic microrefrigerator using a superconducting flux qubit. Adiabatic flux modulation and thermalisation can be used to transfer energy from the standard thin film resistance of the lower temperature to another at a higher temperature. Include the hot resistor as part of the highfrequency LC resonator and the cold as part of the low frequency oscilator while keeping both circuits under the damped mode, which enhance Photonic heat conduction's frequency selection. In an experimentally practical context we talk about the output of the computer. The complementarity of information and Thermodynamic Entropy is shown by this system as quantic bit erasure directly relates to resistance cooling.
By longitudinal combination of two superconducting resonators, we realise a superconducting circulus analogue to the generic Hamilton cavity-optomechanical, which are of a different order of dimension. Longitudinal connections are achieved by incorporating a superconducting quantum interference into a high frequency resonator, so that the frequency of its resonance depends upon the zero-point current fluctuations of the nearby low frequency LC resonator. By using sideband drive fields the intrinsic coupling power is increased by controlling the amplitude of the drive field by around 15 kHz to 280 kHz. Our findings pave the way for the examination in a completely superconducting platform of optomechanical effects and allow quantum optical experiments with radiofrequencybands in which photons are unexplored. We consider a design for a cyclic microrefrigerator using a superconducting flux qubit. Adiabatic flux modulation and thermalisation can be used to transfer energy from the standard thin film resistance of the lower temperature to another at a higher temperature. Include the hot resistor as part of the highfrequency LC resonator and the cold as part of the low frequency oscilator while keeping both circuits under the damped mode, which enhance Photonic heat conduction's frequency selection. In an experimentally practical context we talk about the output of the computer. The complementarity of information and Thermodynamic Entropy is shown by this system as quantic bit erasure directly relates to resistance cooling.
We consider a design for a cyclic microrefrigerator using a superconducting flux qubit. Adiabatic modulation of the flux combined with thermalization can be used to transfer energy from a lower temperature normal metal thin film resistor to another one at higher temperature. The frequency selectivity of photonic heat conduction is achieved by including the hot resistor as part of a high frequency LC resonator and the cold one as part of a low-frequency oscillator while keeping both circuits in the underdamped regime. We discuss the performance of the device in an experimentally realistic setting. This device illustrates the complementarity of information and thermodynamic entropy as the erasure of the quantum bit directly relates to the cooling of the resistor.
We realize a superconducting circuit analog of the generic cavity-optomechanical Hamiltonian by longitudinally coupling two superconducting resonators, which are an order of magnitude different in frequency. We achieve longitudinal coupling by embedding a superconducting quantum interference device into a high frequency resonator, making its resonance frequency depend on the zero point current fluctuations of a nearby low frequency LC resonator. By applying sideband drive fields we enhance the intrinsic coupling strength of about 15 kHz up to 280 kHz by controlling the amplitude of the drive field. Our results pave the way towards the exploration of optomechanical effects in a fully superconducting platform and could enable quantum optics experiments with photons in the yet unexplored radio frequency band.
I describe my contributions towards a hybrid quantum system that would have coupled 87Rb atoms to a superconducting device. I first discuss my work coupling an optical fiber to a translatable thin-film LC lumped-element superconducting Al microwave resonator operating at 100 mK in a dilution refrigerator. The LC resonators had resonance frequencies f0 of 6.15 GHz, quality factors Q of 1.5 x 105 to 6.5 x 105 at high powers, and were mounted inside a superconducting aluminum 3D cavity with a resonance frequency of 7.5 GHz and Q of 8 x 103. An optical microfiber (60 µm diameter) passed through a hole in the 3D cavity near the LC resonator. The 3D cavity was mounted on an x-z attocube-translation stage that allowed the LC resonator to be moved relative to the fiber. The resonator’s f0 and Q were affected both by the fiber dielectric perturbing the resonator’s electric field and from scattered light from the fiber. I measured both effects as a function of fiber-resonator position. I modeled the resonator’s optical response by accounting for optical production, recombination, and diffusion of quasiparticles and the non-uniform position-dependent illumination of the resonator. Using the model, I extracted key parameters describing quasiparticles in the resonator. The hybrid quantum system requires the 87Rb and LC resonator resonance to be tuned to the same frequency. I describe our LC resonator tuning method which moves a superconducting Al pin into the resonator’s electric field, decreasing the resonator capacitance and increasing its resonance frequency up to 137 MHz. This was done at 15 mK using an attocube translation stage. I also investigated two-level system (TLS) defects in an LC resonator by applying a dc voltage. I describe a model in which the TLS causes a capacitive perturbation to the resonator rather than the ‘standard’ electric-dipole coupling model. I use this model of a capacitive TLS or cTLS, to describe intermittent telegraph noise measured in the transmission S21 through the resonator. I measured shifts in f0 of more than 6 kHz corresponding to a cTLS fluctuating its capacitance contribution by 430 zF.
Superconducting qubits are fabricated "loss-free" electrical circuits on a chip with size features of tens of nanometers. If cooled to cryogenic temperatures below -273 °C they behave as quantum elements, similar to atoms and molecules. Such a qubit can be manipulated by fast-oscillating magnetic fields and its resulting quantum state can be measured using a proper magnetic detector. These qubits could be the basic elements for a quantum processor. To that order, multiple qubits have to controllably interact, and to that purpose very high quality resonators are fabricated on the same chip. Effectively the interaction results from the phase-coherent exchange of a single photon between qubit and resonator. In this way it is highly analogous to the so-called cavity QED in atomic physics where single atoms couple to a single trapped photon, all inside a cavity resonator. In this thesis, a superconducting flux qubit has been coupled to an LC resonator and coherent exchange of a single photon between qubit and resonator has been achieved. A striking option in these superconducting circuits, not attainable in "common" atomic cavity-QED, is that the interaction between qubit and photon can be made very large, up to the limit that one no longer can talk about the qubit and resonator as such. This limit requires a fully different description and it leads to novel effects, e.g. in the energy spectrum of the qubit-resonator composite. The Bloch-Siegert spectral shift is experimentally demonstrated in this thesis. As a small but critical technical aside a new type of control line filter has been developed, which allows strong suppression of excess electrical noise that forms a threat for qubit coherence. Having two modes of operation, it shorts all low-frequency noise if control is idle while being transparent if control is active, where short or open is determined by the control line signal level itself.
Advancements in the field of cavity quantum electrodynamics (c-QED) have deepened understanding of quantum phenomena, enabled reliable Josephson junction-based devices, and facilitated their integration with other quantum technologies to explore new physics and applications. Motivated by these developments, this thesis aims to construct a testbed for studying quantum thermodynamics using a superconducting flux qubit. The flux qubit is particularly suited for thermodynamic experiments due to its strong anharmonicity and its galvanic coupling architectures that facilitate efficient energy transport. In this thesis, the on-chip components include harmonic oscillators realized as superconducting resonators, a strongly nonlinear superconducting flux qubit, two copper thermal reservoirs modelled as Johnson–Nyquist noise sources and NIS thermometers, integrated on a highly resistive silicon platform that acts as a phonon bath. These components enable the study and optimization of heat transport between the metallic reservoirs, mediated by the quantum circuit, with the flux qubit as the central, flux-tunable working substance. Heat transport through the qubit occurs via sequential excitation and relaxation cycles between its ground and excited states, where excitation extracts heat equal to the qubit’s energy gap from the hot reservoir, while relaxation releases the same energy into the cold reservoir. Enhancing the thermal device’s performance critically depends on the coupling strength between on-chip components, particularly between the qubit and resonator. This thesis commences with the investigation and demonstration of a robust qubit–resonator coupling design that achieves the ultrastrong regime experimentally. Building on this result, the developed architecture is extended to connect the qubit with two identical resonators, symmetrically positioned on the two sides. These resonators are, in turn, coupled to metallic reservoirs, enabling the first ever demonstration of flux qubit-controlled heat transport between the two reservoirs with excellent device performance. Added geometric asymmetry in the coupler, combined with the flux qubit’s strong anharmonicity, enables the successful demonstration--presented in this thesis--of a non-reciprocal device such as the Microwave Quantum Diode, which, together with the reservoirs, could potentially form an efficient thermal diode. Finally, the thesis concludes with a brief outlook on future directions and ongoing experiments that build on the flux qubit–based testbed developed here for exploring quantum thermodynamic phenomena and device applications.
Microscale and nanoscale mechanical resonators have been used in advanced technological applications, from high precision time keeping and mass sensing, to processing high frequency signals in mobile communications. In the last few decades, they have been an important part of progress in the field of quantum information and metrology and have been proposed as quantum memories or transducers for measuring or connecting different types of quantum systems. The field of cavity optomechanics and electromechanics is concerned with coupling the electromagnetic field of a resonant optical cavity or electrical circuit to mechanical motion. These systems provide potential means to control and engineer the state of a mechanical object at the quantum level. This thesis contains the description of mechanical systems in megahertz to a few hundred megahertz frequency range formed by nano-fabricating photonic, phononic, and electrical circuits on a chip. These structures are designed to provide a large radiation pressure coupling between mechanical motion and electromagnetic fields to address and manipulate motional degrees of freedom. Qualitatively novel quantum effects are expected when one takes a step beyond linear coupling and exploits higher order interactions. To that end, we integrate electrical, mechanical and photonic structures in a multimode photonic crystal structure to observe "x2-coupling", where the optical cavity frequency is coupled to the square of the mechanical displacement. Moreover, we have developed two integrated on-chip platforms based on Si3N4 and Si nanomembranes capable of interfacing superconducting qubits and optical photons and realizing reversible microwave-to-optical conversion. We employ radiation pressure to cool these mechanical resonators to their quantum ground state. Finally, we demonstrate a form of electromechanical crystal for coupling microwave photons and hypersonic phonons of frequency ωm/2π = 0.425 GHz by capacitively coupling a phononic crystal acoustic cavity to a superconducting microwave resonator. Moving to higher frequency acoustic cavities not only facilitates the integration of electromechanical circuits and nanophotonic systems capable of operation in the resolved sideband limit of optomechanics for noise-free quantum signal conversion, but it opens up the possibility of using phonons as information carriers via phononic circuits. Utilizing a two-photon resonance condition for efficient microwave pumping and phononic bandgap shield to eliminate acoustic radiation, we achieve large cooperative electromechanical coupling (C ≈ 30) and intrinsic decay time of 2.3 ms. Moreover, electrical read-out of the phonon occupancy shows that the acoustic mode thermalizes close to its quantum ground-state of motion (phonon occupancy nm=1.5) at a fridge temperature of Tf = 10 mK. We conclude by considering several designs and fabrication improvements to the hypersonic electromechanical crystals that would enable them to perform quantum conversion between the electrical and acoustic domain.