Stanford EE

Mitigating Environmental Effects on Superconducting Qubits: Quasiparticle Poisoning from Radioactivity, Cosmic Rays, and Thermal Backgrounds

Noah Kurinsky

Zoom ID: 919 1812 2594; Password: 002341

Abstract: While significant progress has been made towards the first viable quantum computer, significant barriers still prevent us from scaling from the 10s to thousands of qubit regimes needed long-term to realize practical quantum algorithms. In particular, individual qubit coherence times have stalled at around 1 ms for superconducting qubits, limited largely by immature and inconsistent fabrication techniques, as well as inefficient quasiparticle cooling, which keeps the qubits much hotter than their environments and leads to month-scale cooling times. I the last few years, we have identified a number of sources of quasiparticle poisoning from a combination of charge, phonon, and photon induced heating mechanisms, and we have begun to engineer mitigations that reduce the spatial correlation for radiation-induced errors. To make significant progress, we need to push fabrication techniques to more complex scales such as can be achieved in the new SLAC Detector Microfabrication Facility (DMF), and implement an array of mitigations, including gap engineering in junction, active quasiparticle cooling, substrate field shaping, and phonon mitigation structures. These new techniques will combine to produce long-lived, better thermalized, spatially independent individual qubits that can pave the way towards more scalable quantum processors. In addition, these mitigations also present new opportunities in quantum sensing at the meV scale synergistic with HEP scientific priorities for the next decade, and I will discuss recent developments in utilizing strongly coupled transmon qubits to produce pair-breaking photon and phonon counters. I will conclude by putting this program into the larger context of public and industrial efforts in the quantum computing space, and discussing how this program fits into the work being done on both sides of the funding divide.