Quantum Acoustics with high-overtone bulk resonators and superconducting qubits: High-Q planar devices, phononlasers, and quantum ghosts

The field of quantum acoustics studies high frequency sounds generated at low temperatures such that quantum mechanical effects become relevant. The studies mainly revolves around propagating quantized sound waves, or phonons, a collective excitation of atoms in solids or liquids. In quantum acoustics, the engineering and design tools described...

Optimizing quantum error correction for superconducting qubit processors

The theory of quantum mechanics describes many phenomena that may initially seem to be counter-intuitive and, in some cases, impossible, given the understanding of classical mechanics that most of us are more intimately familiar with. Following its initial introduction, there was a great deal of debate among scientists regarding the predictions...

Experimental Quantum Simulation with noisy intermediate-scale superconducting processors

Superconducting qubits have seen a tremendous progress in the last two decades, and yet they remain unable to extract quantum advantage for application scenarios. While algorithms like Shor’s demonstrate quantum advantage in theory, they do not seem to fit modern noisy quantum processors. Then, in order to achieve quantum advantage either modern...

Bi-Directional Tuning of Josephson Junction Resistance

One of the main components used in superconducting quantum chips is the Josephson junction. Currently when fabricating Josephson junctions, the resistance uniformity at wafer-scale is not optimal. It is also known that an annealing process can alter the junction resistance and with it the qubit frequency. However, laser annealing has only shown...

Mitigating Leakage and Noise in Superconducting Quantum Computing

Computers are used all over the place to perform tasks ranging from sending an email to running some complicated numerical simulation. That is brilliant of course, because computers enable us to solve a lot of problems in the world in this way. At the same time, for some of those problems, not even powerful supercomputers are enough to get the...

Cavity magnonics

Cavity magnonics deals with the interaction of magnons — elementary excitations in magnetic materials — and confined electromagnetic fields. We introduce the basic physics and review the experimental and theoretical progress of this young field that is gearing up for integration in future quantum technologies. Much of its appeal is derived...

In-situ bandaged Josephson junctions for superconducting quantum processors

Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits—the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so...

Encoding a Qubit into an Oscillator with Near-Term Experimental Devices

A universal, large-scale quantum computer would be a powerful tool with applications of high value to mankind. For example, such a computer could significantly speed up the search for new medications or materials. However, the error rates of current qubit designs are simply too large to enable interesting computations. Therefore, both error...

Towards scalable bosonic quantum error correction

We review some of the recent efforts in devising and engineering bosonic qubits for superconducting devices, with emphasis on the Gottesman-Kitaev-Preskill (GKP) qubit. We present some new results on decoding repeated GKP error correction using finitely-squeezed GKP ancilla qubits, exhibiting differences with previously studied stochastic...

Hamiltonian quantum computing with superconducting qubits

We consider how the Hamiltonian Quantum Computing scheme introduced in (2016 New J. Phys. 18 023042) can be implemented using a 2D array of superconducting transmon qubits. We show how the scheme requires the engineering of strong attractive cross-Kerr and weak flip-flop or hopping interactions and we detail how this can be achieved. Our...

Fast, High-Fidelity Conditional-Phase Gate Exploiting Leakage Interference in Weakly Anharmonic Superconducting Qubits

Conditional-phase (cz) gates in transmons can be realized by flux pulsing computational states towards resonance with noncomputational ones. We present a 40 ns cz gate based on a bipolar flux pulse suppressing leakage (0.1%) by interference and approaching the speed limit set by exchange coupling. This pulse harnesses a built-in echo to...

Scalability and modularity for transmon-based quantum processors

This thesis mainly summarizes two experiments that relate to building a quantum computer out of superconducting transmon qubits. Transmon qubits have emerged as one of the foremost solid state qubits, realizing processors with more than ten qubits and demonstrating small scale quantum algorithms as well as quantum error correction schemes. Right...

A magnetic field insensitive graphene transmon qubit

Majorana zero modes have been proposed as building blocks of intrinsically fault-tolerant quantum computers. Currently, externally applied magnetic fields are necessary to induce Majorana zero modes in carefully engineered systems. Topological qubit state readout is realized by parity sensing of Majorana islands. However, fast and high fidelity...

Feedback control of superconducting quantum circuits

Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback control of superconducting qubits based on...

On the Quantum Measurement of Superconducting Flux Qubits