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arXiv:2310.13454

Efficient General Waveform Catching by a cavity at a Virtual Absorbing Exceptional Point

Asaf Farhi, Wei Dai, Seunghwi Kim, Andrea Alù, A. Douglas Stone

Published Oct 20, 2023• 0 citations
arXivHTMLPDF

Abstract

State transfer and photon detection are fundamental processes that have direct implications in fields such as quantum computing and photonic circuits. However, while naturally emitted photons decay exponentially in time, to perfectly capture a photon its envelope should increase exponentially to match the time-reversed response of the absorbing cavity. Here we show that a cavity at a virtual absorbing exceptional point captures additional temporal orders of an incoming waveform, resulting in efficient passive state transfer and photon detection. This approach paves the way for state transfer at optical frequencies and efficient detection of a spontaneously emitted photon.

DOI
10.48550/arxiv.2310.13454

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State transfer and photon detection are fundamental processes that have direct implications in fields such as quantum computing and photonic circuits. However, while naturally emitted photons decay exponentially in time, to perfectly capture a photon its envelope should increase exponentially to match the time-reversed response of the absorbing cavity. Here we show that a cavity at a virtual absorbing exceptional point captures additional temporal orders of an incoming waveform, resulting in efficient passive state transfer and photon detection. This approach paves the way for state transfer at optical frequencies and efficient detection of a spontaneously emitted photon.
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We demonstrate the ability to control spontaneous emission from a superconducting qubit coupled to a cavity. The time domain profile of the emitted photon is shaped into a symmetric truncated exponential. The experiment is enabled by a qubit coupled to a cavity, with a coupling strength that can be tuned in tens of nanoseconds while maintaining a constant dressed state emission frequency. Symmetrization of the photonic wave packet will enable use of photons as flying qubits for transferring the quantum state between atoms in distant cavities.
Being able to reliably transfer the quantum state from one system to another is crucial to developing quantum networks. A standard way to accomplish this transfer of information is by making use of an intermediate information carrier (e.g., a photon) that is emitted by the first system and absorbed by the second. For such a scenario one can develop an effective description by eliminating the intermediate degrees of freedom, which yields an effective direct coupling between the two systems. If, however, the spectral properties of the two systems are different, the photon's time-frequency shape needs to be appropriately modified before it reaches the second system. We study here the effective description that results when we thus manipulate the intermediate photon. We examine a unitary transformation UUU that time reverses, frequency translates, and stretches the photon wave packet. We find that the concomitant modifications to the effective description can best be understood in terms of a change to the state's time argument $\ensuremath{\rho}(t)={\ensuremath{\rho}}_{1}(\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{t})\ensuremath{\bigotimes}{\ensuremath{\rho}}_{2}(t)$, where $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{t}$ is a fictitious time for the first system that is stretched and runs backward. We apply this theory to three-level $\mathrm{\ensuremath{\Lambda}}$ systems inside optical cavities, and we numerically illustrate how performing the unitary transformation UUU results in improved quantum state transfer.
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