Interfacing broadband photonic qubits to on-chip cavity-protected rare-earth ensembles

Abstract

Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level—a technique to suppress ensemble decoherence due to inhomogeneous broadening. The protected Rabi oscillations between the cavity field and the atomic super-radiant state enable ultra-fast transfer of photonic frequency qubits to the ions (∼50 GHz bandwidth) followed by retrieval with 98.7% fidelity. With the prospect of coupling to other long-lived rare-earth spin states, this technique opens the possibilities for broadband, always-ready quantum memories and fast optical-to-microwave transducers.

Nanophotonic rare-earth quantum memory with optically controlled retrieval

“…N=0). This expression assumes negligible correlation between ions of different frequencies, which is valid for an inhomogeneous ensemble that is coupled to a cavity below the strong collective coupling regime (15).…”

Material platforms for integrated quantum photonics

“…Rare-earth doped Y 2 SiO 5 have been used to demonstrate efficient quantum information storage [155] and operation at telecom wavelength [156]. Integration of such quantum memories onto a chip has been prototyped using the direct writing technique [157] and free-standing nanobeam waveguides [134] (see Figure 5e), resulting in frequency-encoded qubit storage with fidelity approaching 99% [158]. For a recent review of quantum memories, see Ref.…”

Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift

“…Thus, there is significant impetus to develop other methods to increase photon-ion interactions [13][14][15][16][17]. One solution is to fabricate photonic crystal resonators directly in REI crystals [15,[18][19][20][21]. A large increase in photon-ion coupling is achieved through cavity enhancement of the optical transition [22] and strong * faraon@caltech.edu mode confinement [14,[23][24][25][26].…”