Building a Bosonic Microwave Qubit
Doctoral thesis, 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.
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
Author
Marina Kudra
Chalmers, Microtechnology and Nanoscience (MC2), Quantum Technology
Decoherence benchmarking of superconducting qubits
npj Quantum Information,;Vol. 5(2019)
Journal article
Stability of superconducting resonators: Motional narrowing and the role of Landau-Zener driving of two-level defects
Science advances,;Vol. 7(2021)
Journal article
High quality three-dimensional aluminum microwave cavities
Applied Physics Letters,;Vol. 117(2020)
Journal article
Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences
PRX Quantum,;Vol. 3(2022)
Journal article
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-
Journal article
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.
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.
Areas of Advance
Nanoscience and Nanotechnology
Subject Categories
Other Physics Topics
Nano Technology
Infrastructure
Nanofabrication Laboratory
ISBN
978-91-7905-780-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5246
Publisher
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