Classical computing relies on large arrays of robust miniaturized bits. Similarly, the development of useful quantum computing requires millions of low-footprint error-tolerant qubits. Current state-of-the-art superconducting qubits are not compatible with this approach as they rely on large device areas to increase qubit lifetimes and reduce noise. This limits the practicality of building a scalable superconducting quantum computer given size constraint. We explore an alternative to this limitation, where we predict both orders-of-magnitude reduction in qubit footprint and...
We are developing high-efficiency microwave impedance transformers for microwave-to-optical quantum transducers. Our goal is to match a standard 50 Ω microwave environment to a novel high-impedance electro-optic (EO) device based on a 20 kΩ thin-film lithium niobate (TFLN) traveling-wave modulator. The high impedance increases the microwave field in the EO device and improves the overall transduction efficiency. We will use a Klopfenstein taper design, as it provides low reflection with a compact length over a broad bandwidth. We target 4–8 GHz operation and near-unity coupling to the 20...
Superconducting transmon qubits are one of the most promising platforms to realize fault-tolerant quantum computing and allow a rich parameter space of highly configurable qubit properties with various circuit elements. Ultra thin amorphous oxide tunnel barriers (such as Al/AlOx/Al) known as Josephson junctions (JJ) provide essential nonlinearity to the qubit energy landscape. Precise control over the morphology of these thin amorphous oxide tunnel barriers remains a significant challenge despite its critical role in determining structural and transport properties. Furthermore, materials...
Color centers in solid-state materials are promising candidates as single-photon emitters for quantum information technologies. For color centers in silicon, ion implantation and subsequent annealing are used to create emitters in wafers at a desired density. However, ion implantation introduces damage and additional defects into the silicon lattice, potentially impacting charge environments local to color centers. In this project, we focus on the creation of silicon T centers, which are point defects composed of two carbon atoms, and one hydrogen atom. We propose to use epitaxially grown...
Quantum transduction between microwave and optical frequencies is a fundamental building block for scaling up quantum systems. However, the optical nonlinearities upon which transducers are built are fundamentally weak, limiting their efficiency. In this project we are developing a novel transducer architecture leveraging the quantum-confined Stark effect which enables nonlinearities enhanced by orders of magnitude.
Yuan is a postdoctoral researcher in the Quantum Devices Group led by Prof. Alp Sipahigil at UC Berkeley. His current research focuses on superconducting quantum devices. He earned his PhD in Physics in 2026 from JILA and the University of Colorado Boulder, where he studied solid-state quantum optics using optically active semiconductor quantum dots. He received his BS from Peking University in 2019.
Xiaoya Chen is a Ph.D. student in Electrical Engineering and Computer Sciences at UC Berkeley, where she is advised by Alp Sipahigil in the Quantum Devices Group. Her research centers on superconducting quantum hardware. Xiaoya received her B.S. in Electrical Engineering with honors from University of California, Los Angeles, where she conducted research in the CHIPS Lab.
Kerry Yu is a Ph.D. candidate in Electrical Engineering and Computer Sciences (EECS) at UC Berkeley, advised by Prof. Alp Sipahigil. He earned his M.Sc. in Electrical and Computer Engineering from UCLA and High Honors B.Sc. in EECS from UC Berkeley. His current research focuses on the intersection between microwave and phononic engineering to mitigate the decoherence of superconducting qubits. Kerry is also a recipient of the NSF Graduate Research Fellowship.
Disordered superconductors provide access to a unique regime of superconducting quantum circuits due to their large kinetic inductance, strong intrinsic nonlinearity, and high characteristic impedance. These properties enable compact microwave structures with strong electric field confinement, opening new opportunities for engineered light–matter interactions in reduced footprints. We are developing a DC-tunable, high-impedance superconducting nanowire platform based on TiN, a strongly disordered superconductor. The large kinetic inductance of TiN nanowires enables characteristic...
Superconducting qubits are a leading platform for scalable quantum computing. The transmon qubit, consisting of a Josephson junction (JJ) shunted by a coplanar capacitor, is widely adopted due to its robustness against charge noise. However, its scalability is limited by the large footprint and dielectric losses at material interfaces. The merged-element transmon (MET) was introduced to enable a more compact architecture, yet in current implementations, although the JJ area can be reduced to ~3 µm², the coplanar capacitor still occupies ~100 µm². Moreover, its planar geometry generates...
