Overview

Qubits are typically some form of two-state system (an electron spin up or down, an atom with two energy levels, a superconducting wire with or without current), which can be in either one of the two states, or a superposition of both states at once.  If a QIS “device” with multiple qubits can be sufficiently isolated from the environment, those qubits can be entangled, so they have a shared quantum state which evolves in such a way as to perform a desired computation.  When the computation finishes, the result can be read out as a measurement of the state of the system.

Our research addresses the challenge of decoherence in quantum computing, where environmental factors, such as radiation, disrupt the stability of qubits. The hypothesis is that energy from external sources enters a device, propagates through the substrate on which the qubit resides, interacts with the superconducting component of the qubit to break Cooper pairs into quasiparticles which can cause a change of state of the qubit. This makes devices vulnerable to energy deposits from sources like cosmic rays or radioactivity. We use simulations to understand and mitigate these effects.

With PNNL and MIT we are using G4CMP to develop a chip design optimized for producing and tracking controllable bursts of phonons, and observing their effect on individual qubits.  With SLAC, we are expanding the features of G4CMP to support a wider variety of qubit and energy sensor designs, including transmons and MKIDs, and additional materials beyond germanium and silicon crystals.