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Viewpoint: Superconducting Qubits Are Getting Serious

Matthias Steffen

Published Dec 5, 2011• 3 citations
OpenAlex

Abstract

When placed inside a 3D electromagnetic cavity, a superconducting qubit can be made potentially more useful because of its large size and long coherence time.

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In order to build a useful quantum computer, qubits with long coherence times are needed. Longer coherence times mean that more qubit operations can be performed reliably, which is essential for executing complex quantum algorithms. Recently, there has been significant progress in this field and state-of-the-art superconducting qubits have reached relaxation and dephasing times near the millisecond range. However, it would still be highly beneficial to improve qubit coherence times even further to eventually move forward from the noisy intermediate-scale quantum era. One potential way to achieve this improvement is to utilize a superconducting three-dimensional (3D) cavity as part of a qubit design where nonlinearity is realized with some structure inside the cavity. These cavities can have extremely high quality factors which shows potential for long qubit relaxation times even in the range of tens of milliseconds. In this thesis, we present and experimentally test a novel unimon-type qubit design based on a vacuum-gap Josephson junction inside a superconducting 3D cavity resonator. The junction is located at the center of a high-purity aluminum vacuum cavity, between two pillars extending from the top and the bottom. It is formed with a 3D structure by breaking a thin neck into two parts leaving a vacuum gap between them which forms the insulating layer of the junction. In order to control the vacuum-gap distance, the bottom of the cavity can be moved using a screw and the top wall is controlled using a high-precision cryogenic actuator. We present design simulations, conduct preliminary experiments on the moving of the cavity walls and carry out room-temperature spectroscopy measurements to identify the resonant modes and their quality factors. The obtained experimental results are quite limited due to certain issues with the first prototypes of the design. However, identifying these issues provides pivotal information for improving the design in the future. Although the preliminary results show that further research is needed, this thesis provides a solid base for developing the device further towards a high-coherence superconducting qubit.

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Technologies for a long-lived 3D multimode microwave cavity are disclosed. In the illustrative embodiment, a series of overlapping holes are drilled into a monolithic block of aluminum forming a cavity. The dimensions of the cavity formed by the overlapping holes can be made long by drilling a long series of holes in a row and can be made high by drilling holes a certain depth into the cavity. if two dimensions of the cavity are bigger than the diameter of the holes used to create the cavity, then the cavity can support electromagnetic waves that cannot propagate through the holes, leading to a long lifetime in the cavity. A superconducting qubit or other non-linear element can be inserted into the cavity, which can controllably interact with each of several modes of the cavity. In this way, the modes of the cavity can act as components in a quantum memory.

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Design and processing considerations for superconducting qubits coupled to multiple 3D cavities

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Bulletin of the American Physical Society•Mar 2, 2015•0 citations

TECHNOLOGIES FOR LONG-LIVED 3D MULTIMODE MICROWAVE CAVITIES

David Schuster, Naik Ravi, Srivatsan Chakram

Technologies for a long-lived 3D multimode microwave cavity are disclosed. In the illustrative embodiment, a series of overlapping holes are drilled into a monolithic block of aluminum forming a cavity. The dimensions of the cavity formed by the overlapping holes can be made long by drilling a long series of holes in a row and can be made high by drilling holes a certain depth into the cavity. If two dimensions of the cavity are bigger than the diameter of the holes used to create the cavity, then the cavity can support electromagnetic waves that cannot propagate through the holes, leading to a long lifetime in the cavity. A superconducting qubit or other non-linear element can be inserted into the cavity, which can controllably interact with each of several modes of the cavity. In this way, the modes of the cavity can act as components in a quantum memory.

•Jun 15, 2022•0 citations
In order to build a useful quantum computer, qubits with long coherence times are needed. Longer coherence times mean that more qubit operations can be performed reliably, which is essential for executing complex quantum algorithms. Recently, there has been significant progress in this field and state-of-the-art superconducting qubits have reached relaxation and dephasing times near the millisecond range. However, it would still be highly beneficial to improve qubit coherence times even further to eventually move forward from the noisy intermediate-scale quantum era. One potential way to achieve this improvement is to utilize a superconducting three-dimensional (3D) cavity as part of a qubit design where nonlinearity is realized with some structure inside the cavity. These cavities can have extremely high quality factors which shows potential for long qubit relaxation times even in the range of tens of milliseconds. In this thesis, we present and experimentally test a novel unimon-type qubit design based on a vacuum-gap Josephson junction inside a superconducting 3D cavity resonator. The junction is located at the center of a high-purity aluminum vacuum cavity, between two pillars extending from the top and the bottom. It is formed with a 3D structure by breaking a thin neck into two parts leaving a vacuum gap between them which forms the insulating layer of the junction. In order to control the vacuum-gap distance, the bottom of the cavity can be moved using a screw and the top wall is controlled using a high-precision cryogenic actuator. We present design simulations, conduct preliminary experiments on the moving of the cavity walls and carry out room-temperature spectroscopy measurements to identify the resonant modes and their quality factors. The obtained experimental results are quite limited due to certain issues with the first prototypes of the design. However, identifying these issues provides pivotal information for improving the design in the future. Although the preliminary results show that further research is needed, this thesis provides a solid base for developing the device further towards a high-coherence superconducting qubit.
Technologies for a long-lived 3D multimode microwave cavity are disclosed. In the illustrative embodiment, a series of overlapping holes are drilled into a monolithic block of aluminum forming a cavity. The dimensions of the cavity formed by the overlapping holes can be made long by drilling a long series of holes in a row and can be made high by drilling holes a certain depth into the cavity. if two dimensions of the cavity are bigger than the diameter of the holes used to create the cavity, then the cavity can support electromagnetic waves that cannot propagate through the holes, leading to a long lifetime in the cavity. A superconducting qubit or other non-linear element can be inserted into the cavity, which can controllably interact with each of several modes of the cavity. In this way, the modes of the cavity can act as components in a quantum memory.
Technologies for a long-lived 3D multimode microwave cavity are disclosed. In the illustrative embodiment, a series of overlapping holes are drilled into a monolithic block of aluminum forming a cavity. The dimensions of the cavity formed by the overlapping holes can be made long by drilling a long series of holes in a row and can be made high by drilling holes a certain depth into the cavity. If two dimensions of the cavity are bigger than the diameter of the holes used to create the cavity, then the cavity can support electromagnetic waves that cannot propagate through the holes, leading to a long lifetime in the cavity. A superconducting qubit or other non-linear element can be inserted into the cavity, which can controllably interact with each of several modes of the cavity. In this way, the modes of the cavity can act as components in a quantum memory.