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arXiv:1803.04711 · Applied Physics Letters

Compact 3D quantum memory

Edwar Xie, Frank Deppe, Michael Renger, Daniel Repp, Peter Eder, Michael Fischer, Jan Goetz, Stefan Pogorzalek, Kirill G. Fedorov, Achim Marx, Rudolf Groß

Published May 14, 2018• 17 citations
arXivHTMLPDF

Abstract

Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well-controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit to both a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. External coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of 6 with a fidelity of approximately 80% determined via quantum process tomography. We also find that this enhancement is not limited by fundamental constraints.

DOI
10.1063/1.5029514

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Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well-controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit to both a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. External coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of 6 with a fidelity of approximately 80% determined via quantum process tomography. We also find that this enhancement is not limited by fundamental constraints.
Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit both to a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. The external coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of 666 with a ZZZ-fidelity of 82%82\%82%. We also find that this enhancement is not limited by fundamental constraints.
Multimode cavity quantum electrodynamics-where a two-level system interacts simultaneously with many cavity modes-provides a versatile framework for quantum information processing and quantum optics. Because of the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of 2 ms across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.
Three-dimensional microwave cavity resonators have been shown to reach lifetimes of the order of a second by maximizing the cavity volume relative to its surface, using better materials, and improving surface treatments. Such cavities represent an ideal platform for quantum computing with bosonic qubits, but their efficient control remains an outstanding problem since the large mode volume results in less efficient coupling to nonlinear elements used for their control. Moreover, this coupling induces additional cavity decay via the inverse Purcell effect that can easily destroy the advantage of a long intrinsic lifetime. Here, we discuss conditions on, and protocols for, efficient utilization of these ultra-high-quality microwave cavities as memories for conventional superconducting qubits. We show that, surprisingly, efficient write and read operations with ultra-high-quality cavities do not require similar quality factors for the qubits and other nonlinear elements used to control them. Through a combination of analytical and numerical calculations, we demonstrate that efficient coupling to cavities with second-scale lifetime is possible with state-of-the-art transmon and superconducting nonlinear asymmetric inductive element devices and outline a route towards controlling cavities with even higher quality factors. Our work explores a potentially viable roadmap towards using ultra-high-quality microwave cavity resonators for storing and processing information encoded in bosonic qubits. Published by the American Physical Society 2024
A promising way to store quantum information is by encoding it in the bosonic excitations of microwave resonators. This provides for long coherence times, low dephasing rates, as well as a hardware-efficient approach to quantum error correction. There are two main methods used to make superconducting microwave resonators: by traditionally machining them out of bulk material and by lithographically fabricating them on a chip in thin film. 3D resonators have few loss channels and larger mode volumes, and therefore smaller participations in the lossy parts, but it can be challenging to achieve high material quality. On-chip resonators can use low-loss thin films, but they confine the field more tightly, resulting in higher participations and additional loss channels from the dielectric substrate. In this work, we present a design in which a dielectric scaffold supports a thin-film conductor within a 3D package, thus combining the low surface participations of bulk-machined cavities with high quality and control over materials of thin-film circuits. By incorporating a separate chip containing a transmon qubit, we realize a quantum memory and measure single-photon lifetimes in excess of a millisecond. This hybrid 3D architecture has several advantages for scaling as it relaxes the importance of the package and permits modular construction with separately replaceable qubit and resonator devices.
Three-dimensional microwave cavities have recently been combined with superconducting qubits in the circuit quantum electrodynamics (cQED) architecture. These cavities should have less sensitivity to dielectric and conductor losses at surfaces and interfaces, which currently limit the performance of planar resonators. We expect that significantly (>10^3) higher quality factors and longer lifetimes should be achievable for 3D structures. Motivated by this principle, we have reached internal quality factors greater than 0.5x10^9 and intrinsic lifetimes of 0.01 seconds for multiple aluminum superconducting cavity resonators at single photon energies and millikelvin temperatures. These improvements could enable long lived quantum memories with submicrosecond access times when strongly coupled to superconducting qubits.
Three-dimensional microwave cavities have recently been combined with superconducting qubits in the circuit quantum electrodynamics architecture. These cavities should have less sensitivity to dielectric and conductor losses at surfaces and interfaces, which currently limit the performance of planar resonators. We expect that significantly (>103) higher quality factors and longer lifetimes should be achievable for 3D structures. Motivated by this principle, we have reached internal quality factors greater than 0.5 × 109 and intrinsic lifetimes of 0.01 s for multiple aluminum superconducting cavity resonators at single photon energies and millikelvin temperatures. These improvements could enable long lived quantum memories with submicrosecond access times when strongly coupled to superconducting qubits.