Abstract
As in conventional computing, memories for quantum information benefit from high storage density and, crucially, random access, or the ability to read from or write to an arbitrarily chosen register. However, achieving such random access with quantum memories in a dense, hardware-efficient manner remains a challenge. Here we introduce a protocol using chirped pulses to encode qubits within an ensemble of quantum two-level systems, offering both random access and naturally supporting dynamical decoupling to enhance the memory lifetime. We demonstrate the protocol in the microwave regime using donor spins in silicon coupled to a superconducting cavity, storing up to four weak, coherent microwave pulses in distinct memory modes and retrieving them on demand up to 2 ms later. This approach offers the potential for microwave random access quantum memories with lifetimes exceeding seconds, while the chirped pulse phase encoding could also be applied in the optical regime to enhance quantum repeaters and networks.
8 More- Received 17 May 2022
- Revised 16 August 2022
- Accepted 31 August 2022
DOI:https://doi.org/10.1103/PhysRevX.12.041014
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Chirping toward a Quantum RAM
Published 7 November 2022
A new quantum random-access memory device reads and writes information using a chirped electromagnetic pulse and a superconducting resonator, making it significantly more hardware-efficient than previous devices.
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Popular Summary
Computing uses different physical systems to represent information, depending on whether it is being processed, stored, or transported; computer memories allow us to retrieve any data entry—in other words, they offer random access. Quantum computing needs similar capabilities. While protocols exist for storing arrays of qubits within spins in cavities or resonators, they lack a practical way to address stored qubits on demand. Here, we present an idea for how to achieve random access and use numerical simulations and experiments to show that the protocol works. The method is practically simple, widely applicable, and likely to be used in future implementations of memories for quantum information.
Spins offer the longest coherence lifetimes of any solid-state system, with coherence lifetimes of seconds or more, and coupling them to superconducting resonators provides a route to storing and retrieving qubits in the form of single microwave photons. Our random-access protocol is based on a simple insight: Frequency-chirped pulses impart phase patterns onto excitations stored in a spin ensemble, and a second identical pulse removes the phase pattern. We use these phase patterns to suppress unwanted emission of the stored states out of the memory and turn them into keys to access specific excitations that have been stored.
By combining this new random-access protocol with advances in spin-cavity coupling strength and coherence time, it will be possible to create a powerful new resource: a chip-based memory able to store many registers of qubits, with high fidelity, for times approaching seconds, with any register retrievable on demand.