Room Temperature Quantum Memories

Entanglement distribution schemes rely on the use of entangled photon pair sources interfaced with in-out QMs (Type II), capable of receiving and storing arbitrary polarization quantum states and releasing them later on demand. Such QMs are needed for high-repetition entanglement swapping operations. We develop Type II QMs with performance thresholds necessary to demonstrate memory advantage.. Our recent experiments have achieved QM systems with 20% single-photon storage efficiencies, 200 microseconds qubit storage times, and >90% qubit retrieval fidelities. Additionally, we have recently demonstrated the first Hong-Ou-Mandel interference of type II QMs. We utilized the adjustable time delay of the memories to counterbalance the asymmetries present in independent communication channels. 

Heralded Quantum Memories

Heralding the storage of entangled photons in QMs after propagating in the fiber links is fundamental to achieving high-repetition entanglement swapping operations. We study how to utilize photon-photon nonlinear atomic mechanisms to demonstrate quantum memory heralding. We have recently demonstrated a nonlinear photon-photon system where the presence of a single-photon level probe field creates a 𝛑-phase shift in the quantum state of a “heralding” signal field. Our approach is based on achieving significant crossed-phase modulation (XPM) for few-photon-level heralding fields interacting with the input photons.

Quantum memory heralding. A sequence of probe photons  (Ωp) and signal (heralding) pulses (Ωs) are sent through an Rb QM. The QM output is then measured on a balanced homodyne detector, and the associated quadrature and phase values are analyzed. (right) The sequence of input pulses. First, we will send a pulsed probe field  (Ωp), with two control fields (Ωc1, Ωc2) creating EIT conditions. Secondly, we will add a pulsed signal (heralding) Ωs field, creating a double-lambda system (bottom left inset). Voltage values of a balanced homodyne detector with a local oscillator tuned to Ωs will be gathered pulse by pulse. Phase information correlated to the presence of a probe photon can then be extracted in quasi-real time.

We also envisage the need to develop networked heralded QMs (NHQMs) that will combine single-photon-level dynamic EIT storage of entangled photons and non-linear phase-phase XPM using FWM to communicate the successful capture of photons in the quantum memory within a larger network. The figure below outlines how we plan to incorperate the aformentions heralding mechinism into the network.

Experimental setup to demonstrate quantum memory advantage. The elementary memory-assisted BSM will include two independent input streams of polarization-entangled photons, two atomic-vapor dual-rail quantum memories, real-time heralding mechanisms based on FWM (bottom right inset), and a BSM setup to evaluate the quantum memory advantage. The BSM intranode at SBU will include a node orchestrator, a network switch, a White Rabbit switch, and two NHQMs. The controlling electronics are driven by the orchestrator, synchronized with the rest of the network. The NHQM electronics interface with the electronics of the memory-heralding FPGA driver, while the memory input is connected to an optical demultiplexer that separates the quantum signals from the classical control signals. The bottom right inset shows the atomic scheme pioneered in our previous work.

To learn more please see Chase Wallace’s presentation on our recent results below:

To learn more about our multiplexed memories see the presentation by Siddharth Sehgal (presented by Chase Wallace) below: