Quantum Frequency Conversion
The successful transmission of entanglement in the network relies on high-efficiency QFCs, to connect the telecom quantum sources with infra-red quantum memories, as well as to establish high-repetition rate entanglement connections between arbitrary points in the network.
We study the dynamics of an atomic 4-level system in a diamond configuration and their effect on the frequency conversion of single-photon-level signals. Here, 795 nm photons are sent to Rb atomic vapor for conversion to 1324 nm. Simultaneously, two laser pumps tuned to Rb lines, one at 780 nm (5S1/2 to 5P3/2) and one at 1367 nm (5P3/2 to 6S1/2) are applied. Our recent experiments have achieved 40% photon conversion efficiency between the 795/1324 nm quantum memory wavelengths. We characterize the frequency conversion efficiency as a function of the atomic system parameters, such as detunings, couplings, and optical depth in a diamond configuration. We will also study the effect of extra re-pumping lasers, coupled to additional ground states, on the frequency conversion efficiency. We also study the noise mechanisms present toward achieving high signal-to-noise (SNR) ratio at the quantum level. Our target is to achieve single-photon level frequency conversion at high efficiency (approx. 70%) with SNRs higher than 10. We will also utilize our dual-rail polarization QMs to explore their integration with this frequency conversion process, aiming to demonstrate the frequency conversion and storage of polarization qubits.
The frequency conversion setup. An Electro-Optic Modulator (EOM) modulates the field envelope of the 795 nm signal. The signal is combined with the two pumps (780nm and 1367 nm), and all three beams are sent to the Rb cell. (Blue box): Diamond atomic scheme used for frequency conversion. The 1367 nm laser is stabilized using an Optical-Optical Double Resonance locking setup. SAS: saturated absorption spectroscopy setup; LD: laser diode; BS: beam splitter; LF: long pass filter; BPD: balanced amplified photodetector; FG1: function generator generating 100kHz laser current modulation signal; FG2: function generator used to generate 10 Hz signal for laser Piezo scanning; LPF: low-pass filter; OSC: monitor oscilloscope; PI: proportional-integral controller.