We’re hiring! The group is now recruiting postdoctoral fellows and research scientists. Learn more about these opportunities and apply through the links below:

Postdoctoral fellowship

Research scientist position

This fall, we are welcoming three new members in the group. Gustave Coulombe (left) is starting his Master’s after completing his Bachelor’s in Engineering Physics at Université Laval. Julien-Pierre Houle (center) is also beginning his Master’s after completing his Bachelor’s in Physics at Université de Sherbrooke. His research will be co-supervised with Professor Cunlu Zhou from the Computer Science Department. Finally, Émile Baril (right) is starting his PhD after completing a Bachelor’s in Physics at Université Laval and a Master’s in Physics at Université de Montréal. Welcome to all three!

How long does it take an open quantum system to reach its steady state? In a large class of classical systems – those which satisfy “detailed balance” – the answer is well-understood. In collaboration with several former group members now working at Alice & Bob and École Normale Supérieure, we show that this result can be extended to open quantum systems which satisfy the quantum analogue of detailed balance. We use it to provide a precise estimate of the bitflip rate of imperfect dissipative cat qubits.

The Kerr cat qubit is a bosonic qubit that exhibits a large noise bias. A larger bias translates into fewer resources required for error correction. Yet recent circuit‑QED experiments show that this bias cannot be made arbitrarily large, and the origin of this limitation has remained unclear. Our work identifies the main culprit: the multimode nature of the Kerr cat circuit shortens its lifetime. Thankfully, our theory also suggests that a large noise bias can be recovered by carefully engineering the qubit’s electromagnetic environment.

Quantum metrology promises to drastically improve signal sensing capabilities throughout a range of scientific fields ranging from biology to physics and engineering. To deliver on this promise, experimental sensing protocols resilient to noise must be developed. In our theoretical work, we propose a displacement sensor that harnesses uncoventional states of light known as Gottesman-Kitaev-Preskill (GKP) states. Our sensor achieves sensitivities close the limit allowed by quantum mechanics, while remaining resilient to noise thanks to the error-correcting properties of GKP states. The protocol can be implemented on a variety of platforms, such as superconducting circuits or trapped ions, and has potential applications in force sensing, waveform estimation, and quantum channel learning.

Transmon qubits are a leading candidate to encode quantum information. Many recent works have shown that the strong voltages used to measure transmon qubits can excite them to more energetic states in an uncontrolled way. In collaboration with the University of Pittsburgh and Yale University, we showed that this effect also limits the speed at which the qubit can be controlled, even when using highly off-resonant low-frequency voltages. Our theory explains observations and provides an avenue for improving quantum control in the near future.

Enjoy the read!

This spring, two new articles involving members of the groupe appear on the arXiv. Below is a brief summary along with the link to access them.

First article : Transmon qubits are a leading candidate to encode quantum information. However, it is known that the strong voltages used to measure these qubits can induce measurement errors by exciting the qubit to a more energetic state. In collaboration with the University of Rochester, we studied these excitations and were able to control them. Our theory explains observations and provides tools to improve measurement in the near future.

Second article : One of the advantages of transmon qubits is their resilience against unavoidable electric noise in their environment. However, it was recently suggested that the measurement of these qubits is not protected against such noise. In collaboration with the Karlsruhe Institute of Technology, we studied the effect of electric noise on transmon measurement. Our theory explains observations and suggests strategies to improve measurement in the near future.

Enjoy the read!

We recently welcomed Rémy Lyscar to the group. Originally from France and currently a first-year Master’s student in Fundamental Physics at the University of Paris-Saclay, he is doing a three-month internship with the group.