We show that a cavity at an absorbing exceptional point captures additional temporal orders of any incoming waveform, resulting in efficient passive state transfer and photon detection.
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.
Resonances associated with complex-frequency poles are ubiquitous across physics and can arise in any open system, ranging from subwavelength particles and cavities to biological structures. When two such resonances coalesce, they form exceptional points (EPs), non-Hermitian singularities known to produce unusual spectral and dynamical behavior. However, the dynamics of the response of such resonances and exceptional points to complex frequency drive remained largely unexplored. Here, we experimentally observe the temporal response of complex-frequency resonances and theoretically study this for exceptional points. We unveil a universal transient phenomenon of open cavities driven at complex frequencies: the system's initial response grows linearly, with enhanced growth at exceptional points (EPs), even though the system is passive and the excitation decays. Closed-form theory for general resonators, extended to higher-order modes, predicts efficient power transfer with t and t2 scaling for complex single poles and exceptional points (EPs), respectively, at all times. We demonstrate these effects in subwavelength optical scatterers and experimentally in an electrical circuit analogue, with excellent agreement, and explore configurations that capture EP-enhanced growth.
The scalability of quantum technologies will depend on the ability to interconnect independent quantum systems through photonic channels. However, heterogeneous quantum platforms emit and absorb photons with widely differing properties, severely limiting inter-node interference and modular connectivity. Here we demonstrate a cold-atom optical quantum memory that simultaneously achieves near-unity storage-and-retrieval efficiency and deterministic temporal adaptation of single photons between arbitrary and programmable input and output pulse waveforms. Operating at high optical depth and within a fully integrated architecture, the system can store photons with durations spanning over three orders of magnitude and reshape them arbitrarily without compromising efficiency, achieving compatibility with many current platforms. By augmenting the role of a quantum memory from a passive storage element to an active programmable photonic interface, our results establish a key building block for scalable entanglement-based quantum networks and modular quantum computing architectures.
A quantum transducer, when working as a microwave and optical entanglement generator, provides a practical way to coherently connect optical communication channels and microwave quantum processors. Recent experiments on a quantum transducer verifying entanglement between the microwave and optical photons show the promise of approaching that goal. While flying optical photons can be efficiently controlled or detected, the microwave photon needs to be stored in a cavity or converted to the excitation of a superconducting qubit for further quantum operations. However, it remains challenging to efficiently capture or detect a single microwave photon with an arbitrary time profile. This work focuses on this challenge in the setting of an entanglement-based quantum transducer and proposes a solution by shaping the optical pump pulse. By Schmidt decomposing the output entangled state, we show that the microwave-optical photon pair takes a specific temporal profile that is controlled by the optical pump. The microwave photon from the transducer can be nearly perfectly absorbed by a receiving cavity with tunable coupling and is ready to be converted to the excitation of superconducting qubits, enabling further quantum operations. Published by the American Physical Society 2024