Building a Bosonic Microwave Qubit
Doktorsavhandling, 2022

Superconducting circuits is a promising platform for quantum computing. Quantum information is usually stored in discrete two-level qubits e.g. in transmon qubits. These qubits are interconnected and placed in grids to form logical qubits, and many logical qubits together form a quantum computer.

In this thesis, we consider encoding quantum information in a resonator instead of the two-level qubit. Resonators can host bosonic modes that have, in principle, an infinite number of quantum levels in which we redundantly can encode a discrete qubit. This makes bosonic qubits hardware efficient, since we can perform error correction directly on a single hardware component, namely the resonator. However, we will still need to use an ancilla two-level qubit to universally control the bosonic qubit. This thesis can be interpreted as an instruction guide on creating a bosonic microwave qubit and it contains the following chapters.

We first introduce the cryogenic setup and the state-of-the-art room-temperature hardware that generates the microwave pulses we need to perform all the experiments in this thesis. We discuss the latest generation of the room-temperature measurement- and control-system we used for both bosonic and discrete variable qubit systems.

We then introduce the hardware components that are needed to form a bosonic qubit, namely a superconducting transmon qubit and a 3D superconducting cavity. We explore the fluctuations of their coherence properties, and we try to understand the sources of noise that limit those properties.

Next, we create arbitrary bosonic states and gates by using interleaved sequences of displacements and optimized selective number-dependent arbitrary phase gates. We characterize a bosonic gate, the X-gate on the binomially encoded qubit, by coherent state process tomography.

We then characterize the selective photon addition gate. We implement this gate by a comb of off-resonant drives that simultaneously excite the qubit and add a photon to the cavity depending on its state. Supplemented by an unconditional qubit reset, this gate is suitable for single photon error correction.

3D cavity

qubit

cubic phase state

continuous variable

circuit QED

bosonic codes

GKP-state

superconducting circuits

Kollektorn (A423), MC2, Kemivägen 9, Chalmers University of Technology, Göteborg, Sweden
Opponent: Prof. Steven Girvin, Eugene Higgins Professor of Physics & Applied Physics, Yale University, USA

Författare

Marina Kudra

Chalmers, Mikroteknologi och nanovetenskap, Kvantteknologi

Decoherence benchmarking of superconducting qubits

npj Quantum Information,;Vol. 5(2019)

Artikel i vetenskaplig tidskrift

High quality three-dimensional aluminum microwave cavities

Applied Physics Letters,;Vol. 117(2020)

Artikel i vetenskaplig tidskrift

Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences

PRX Quantum,;Vol. 3(2022)

Artikel i vetenskaplig tidskrift

M. Kervinen, M. Kudra, S. Ahmed, A. M. Eriksson, F. Quijandría, A. Frisk Kockum, P. Delsing, S. Gasparinetti,"Coherent-state quantum process tomography of continuous-variable gates"

M. Kudra, T. Abad, M. Kervinen, A. M. Eriksson, F. Quijandría, P. Delsing, S. Gasparinetti, "Experimental realization of deterministic and selective photon addition in a bosonic mode assisted by an ancillary qubit"

Measurement and control of a superconducting quantum processor with a fully integrated radio-frequency system on a chip

Review of Scientific Instruments,;Vol. 93(2022)p. 104711-

Artikel i vetenskaplig tidskrift

The second quantum revolution is here. We call it a revolution because we expect that the technologies and devices developed will significantly transform our society. The second quantum revolution promises quantum limited sensing, communication with security guaranteed by the laws of physics, efficient simulation of quantum systems using the well-controlled quantum systems, and computations that are beyond the reach of classical computers - quantum computers. A promising platform for building quantum computers is superconducting circuits. Quantum information is usually stored in discrete two-level qubits, e.g. transmon qubits. These qubits are interconnected and placed in grids to form logical qubits, and many logical qubits together form a quantum computer.

In this thesis, we consider encoding quantum information in many quantum levels of a bosonic mode, instead of the two-level qubit. A 3D cavity is one type of resonator that can host bosonic modes in which we can redundantly encode a discrete qubit. This makes bosonic qubits hardware efficient, since one hardware component, namely the 3D cavity, can host an encoded qubit. However, we will still need to use ancilla two-level qubits to universally control the bosonic qubits.

We start by improving the coherence properties of hardware components that are needed to form a bosonic qubit, namely a superconducting transmon qubit and a 3D superconducting cavity. We explore the fluctuations of coherence properties and we try to establish the sources of noise that limit those properties.

Next, we encode quantum information in arbitrary bosonic states and we implement arbitrary bosonic gates using interleaved sequences of displacement and optimized selective number-dependent arbitrary phase gates. We characterize the bosonic gates by coherent state process tomography.

We then characterize the selective photon addition gate. We implement this gate by a comb of sideband drives that simultaneously excite the qubit and add a photon depending on the cavity state. Supplemented by an unconditional qubit reset, this gate is suitable for single-photon quantum error correction.

Finally, to perform all the before-mentioned experiments, and the experiments we envision for the future, we need state-of-the-art room-temperature hardware. We discuss the latest generation of room-temperature measurement and control system we used for both bosonic and discrete variable qubit systems.

Styrkeområden

Nanovetenskap och nanoteknik

Ämneskategorier

Annan fysik

Nanoteknik

Infrastruktur

Nanotekniklaboratoriet

ISBN

978-91-7905-780-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5246

Utgivare

Chalmers

Kollektorn (A423), MC2, Kemivägen 9, Chalmers University of Technology, Göteborg, Sweden

Opponent: Prof. Steven Girvin, Eugene Higgins Professor of Physics & Applied Physics, Yale University, USA

Mer information

Senast uppdaterat

2023-10-25