“Coherent operations on a chip, challenges and opportunities" |
TYPE | Solid State Institute Seminar |
Speaker: | Dr. Roy Zektzer |
Affiliation: | Postdoctoral Researcher Joint Quantum Institute, University of Maryland and NIST U.S.A. |
Date: | 05.02.2025 |
Time: | 12:30 - 13:30 |
Location: | Solid State Auditorium(Entrance) |
Remark: | Jointly with the faculty of Electrical & Computer Engineering |
Abstract: | Abstract Single photon gates, sources, and detectors are the basic building blocks for quantum computers, simulators, and communications systems [1]. Chip-scale integration of such devices has the advantage of scalability and miniaturization and the opportunity to decrease the interaction volume and improve light-matter interaction. Indeed, sources [1], gates [2] and detectors [1] have been fabricated on chips through the integration of semiconductor quantum dots, cold atoms, and superconducting materials, yet these technologies require significant additional physical infrastructure such as cryostats and magneto-optical trapping. Recently, a simple quantum technology has been demonstrated, the atomic-cladded waveguide [3]. These devices can operate at room temperature and do not require any trapping. The short-time interaction of fast-moving atoms (300 m/s) with a nanoscale optical mode damages the atomic state’s coherence, which can affect metrological applications [4], and may also impact single photon operations. However, it has been suggested that the large coupling strengths in nanophotonics can overcome the excess broadening in warm atoms, so that even single atom-single photon strong coupling in cavity quantum electrodynamics (cavity QED) may be observable [5]. In the talk, I will present an integrated photonics platform that combines air-clad microresonators and Rb vapor, with integrated buried heaters enabling a resonator mode to be locked for long-term stable operation. We demonstrate strong coupling between an ensemble of ≈53 atoms interacting with a high-Q (>4x105) cavity mode, with a many-atom coupling strength g/2π≈1 GHz and cooperativity C≈3.6 achieved. We also study these vapor cavity QED devices at lower atomic density, and we observe saturation effects in the cavity transmission for a few atoms in the cavity near-field (on average) [6]. Finally, to achieve higher cooperativity, we have developed defect mode photonic crystal ring resonators with a 10x reduction in mode volume compared to the basic microring resonators while maintaining Q>105 . To operate such a chip-scale quantum system and others we need integrated light sources as well. Quantum technologies mostly operate at visible wavelengths where high-quality integrated sources have yet to be fully developed. Electrooptic (EO) combs are a great spectroscopic tool, constructing a controllable and tunable set of coherent light sources that generate a connection between optical and RF frequencies. This connection enables fast spectroscopic measurements [7] which we intend to use to study atom-light interaction on chip. We have used the second harmonic generation process (SHG) in a silicon nitride microring resonator (MRR) (enhanced by the photogalvanic effect) to translate an EO comb from telecom to 780nm. To increase the comb signal we have injectionlocked a diode using the EO comb. With only 1nW of EO comb power, we were able to lock the diode and produce a good SNR comb. This new method for amplifying combs will enable high-power EO combs to be produced at various wavelengths where modulators and amplifiers are scarce and to measure low-power combs from materials that have low damage threshold or low saturation powers (such as atoms).
Rubidium is a resonance material and as such maintains much higher nonlinearities than standard dielectrics such as SIN. We have used a four-wave mixing (4WM) effect in Rb to translate an EO comb from 780nm to 420nm. Through further integration and cascaded nonlinear processes, we can then translate high-quality telecom light sources to the visible for quantum devices operation.
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