Subcategory: Physics (not Nanoscience)
Bin Fang - University of Illinois at Urbana-Champaign
Co-Author(s): Shuai Dong, University of Illinois at Urbana-Champaign, IL; Seth Meiselman, Naval Research Lab, DC; Offir Cohen, Virginia O. Lorenz, University of Illinois at Urbana-Champaign, IL
Quantum memories, which store and retrieve quantum states of light, are a critical resource in quantum computing and quantum communication. In this paper, we introduce work towards a THz-bandwidth quantum memory using the off-resonance Raman protocol in hot atomic barium vapor. The advantage of the off-resonance Raman protocol is its capability to store broadband photons, enabling high-bit rates for quantum computing and communication. The bandwidth of the control field determines the storage bandwidth, which can be broad thanks to the off-resonant interaction and is limited mainly by the energy splitting between ground and storage states. The large energy splitting in barium between the ground state and storage state of ~340 THz enables storage of < 100 fs photons, leading to a time-bandwidth product > 1000 and minimal thermal population in the storage state, giving very little noise in single-photon operation. To date, researchers have shown storage of GHz-bandwidth photons in atomic systems and THz-bandwidth photons in molecular and solid state systems, but not broadband storage in the telecom range. Barium has a transition at telecom wavelengths, making it feasible for telecom photon storage. We send attenuated coherent state pulses centered at 560 nm coincident with control field pulses at 1550 nm to a heat-pipe oven containing barium atoms to demonstrate storage. We measure the absorption of the signal due to interaction with the control field by mechanically chopping the signal and control fields and detecting the signal incident on the photodiode with a lock-in amplifier. The signal absorption varies as a function of the time delay between the signal and control field. The system’s current optimal efficiency is about 1% for a control field energy of 22.5 nJ and atomic vapor density of 5.1×1019 m-3. We also measure the efficiency for various control pulse energies and atomic densities, indicating their influence on the memory efficiency. As a next step we are improving the efficiency by increasing the pulse energy of the control field. To achieve this, we pick pulses from the 80 MHz pulse train and send them to an amplifier so that for a given amount of average power the pulse energy can be greatly enhanced by the ratio of the original repetition rate to the picked pulse frequency. In summary, we experimentally demonstrate the potential for an ultra-broadband quantum memory in hot atomic barium vapor based on off-resonance Raman interaction. The broadband feature enables the use of ultrashort pulses for fast quantum operation. It also permits spectral pulse shaping to optimize the efficiency as well as fidelity. With the potential to store broadband telecom photons, we believe this memory should find wide interest and add to the toolbox of future quantum applications.EFRI_vol.docx
Funder Acknowledgement(s): NSF Grant Nos. 1521110 and 1640968
Faculty Advisor: Virginia O. Lorenz, firstname.lastname@example.org
Role: I design and perform the experiment, collect and analyze data.