Junior Quantum Seminar - Hana K. Warner & Matthew Yeh

Please join us for the Junior Quantum Seminar with Hana K. Warner from Harvard University who will give the talk "Optical Interconnects for Microwave Frequency Superconducting Qubits" and Matthew Yeh from Harvard University who will give the talk "Electro-optics does not exist without electronics" on Monday May 12th from 3:30pm to 5:30pm in room BS 260.

PLEASE NOTE: The Junior Quantum Series are for gathering  the junior quantum community of master's students, PhDs and post-docs at EPFL, to create a non-judgmental space were scientific ideas can be shared between peers. This event is not for Professors or senior researchers. 

ABSTRACT:

1. "Optical Interconnects for Microwave Frequency Superconducting Qubits": Superconducting (SC) microwave qubits are a promising platform for realizing a valuable computational resource in a quantum cloud, where superconducting processors are linked via a network to realize the large number of qubits required for practical quantum computing. However, creating this link is challenging due to signal attenuation and noise sensitivity characteristic of their operating frequency. Optical photons, on the other hand, are ideal long-distance information carriers because they exhibit low propagation losses in modern fiber optic networks, are insensitive to thermal noise at room temperature, and modern single photon detectors enable efficient information transfer: furthermore, the high bandwidth and low thermal load of optical fibers means radio-over-fiber techniques can be leveraged to enable dense, low temperature interfaces for qubit control and readout. Here, I will discuss work on using the electro-optic (EO) effect in thin-film lithium niobate (TFLN) to mediate a direct conversion process between microwave and optical radiation. This is ideal for enabling high repetition rates and minimizing the generation of excess noise. By coupling optical resonators in TFLN to SC microwave resonators we enhance the conversion process by orders of magnitude, allowing us to overcome the large energy gap between the two regimes. I will discuss work on developing efficient, low-noise EO transducers used to coherently drive SC processors, as well as progress towards using the devices to create long-haul quantum links between superconducting qubit nodes.  
2. Electro-optics does not exist without electronics": Thin-film lithium niobate has had great success revolutionizing commercial markets for modulators, as well as being a promising candidate material platform for emerging applications such as quantum photonics. Nearly all applications, from the single modulator level to increasingly complex integrated photonic circuits require a bias point. To this end, the linear electro-optic (Pockels) effect seems a natural fit—it is efficient, low-power, and cryo-compatible. However, in practice many complex device phenomena emerge during dc biasing for extended periods of time, complicating the utility of this nominally simple tuning knob. In this talk I will discuss the zoo of phenomena that can be observed in this low-frequency regime, in particular characteristic sources of drift and instability at various device interfaces. By simply changing perspectives to a defect-oriented interpretation more characteristic of well-established semiconductor engineering, we can gain fundamental insights and new approaches into the microscopic origins and possible mitigation techniques for these nonidealities. Finally, I will conclude with some remarks on possible fundamental limitations of electro-optic approaches to phase shifting. 

1. Hana Warner is a Ph.D. candidate in Applied Physics at Harvard University, working with Prof. Marko Lončar as an NSF Graduate Research Fellow. Her current research focuses on developing hardware for quantum and classical transduction between microwave and optical frequencies using integrated photonics and electro-optics. Previously, she received bachelor’s degrees in physics and mathematics at William & Mary where she worked on topics including atomic gradiometry and orbital angular momentum transfer using nonlinear interactions in rubidium vapor.
2.  Matthew Yeh is a PhD candidate in Applied Physics at Harvard University, co-advised by Marko Loncar and Evelyn Hu. His current research is focused on materials engineering of the thin-film lithium niobate quantum photonic platform. Previously, he received a bachelor's degree in Electrical Engineering and Computer Science at the University of California, Berkeley, where he worked on various topics in optoelectronics and exciton physics of 2D materials.