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Alice & Bob Talks at March Meeting 2024

The massive hardware overhead required to implement quantum error correction remains the big roadblock towards the realization of a useful quantum computer.

Cat qubits offer a shortcut to this problem as they require 60 to 200 times less physical resources to implement quantum error correction at scale.

In our talks, the team will present the work on the path to these results.


Coupled scattering parameter calculation for superconducting quantum circuit simulation 

By Mattis Hallen – QPU Designer 

Mattis will present a new method to run microwave simulations for Quantum Processing Units (QPU) design. Microwave simulations on superconducting circuits is a computationally demanding task that is generally handled by decomposing the circuit structure into smaller individual blocks. In this talk we explain how we enable fast design parameter optimization using desktop-level computer hardware.

Monday March 4th, 9:24 am – 9:36 am, Room 200CD


Optimizing transmon readout with dynamiqs, a library for GPU-accelerated and differentiable quantum simulations

Part 1 by Ronan Gautier – Quantum Theorist

Ronan will present a new quantum optimal control method in the context of open quantum systems. Learn how we can apply it to the optimization of transmon readout, one of the remaining bottlenecks of transmon-based quantum computers. Ronan will use dynamiqs to achieve a two-fold improvement in readout time compared to existing methods.

Part 2 by Pierre Guilmin – Quantum Theorist

Pierre will present dynamiqs, a new Python library to simulate closed and open quantum systems. It allows faster simulations of large systems with GPUs. In addition, dynamiqs enables computing gradients based on the evolved quantum state, for calibration and control tasks.

Tuesday March 5, 10:12 am – 10:36 pm, Room 200E


Invited Talk:
Dissipative cat qubits for quantum computing 

By Sébastien Jezouin – Chief of Experiments 

Sébastien will present Alice & Bob advances to build a logical qubit out of dissipative cat qubits. We demonstrate experimentally a cat qubit having at the same time quantum coherences and a bit-flip time of nearly 5 minutes. We also show the first realization of a noise-biased CNOT gate in between 2 cat qubits. 

Wednesday March 6th, 3:00 pm – 3:36 pm, Room 200CD 

Quantum control of a cat-qubit with bit-flip times exceeding ten seconds 

By Adrien Bocquet – Quantum Experimentalist

Adrien will present our latest experiment demonstrating the ability to have a high noise bias in cat qubits and that this is preserved under quantum control for more han 10 seconds. Cat qubits inherent and sustained protection against bit-flips makes of them a hopeful path towards useful quantum systems. 

Wednesday March 6, 3:36 pm – 3:48 pm, Room 200CD

Dissipative stabilization of a squeezed cat qubit 

By Rémi Rousseau – Quantum Experimentalist

Rémi will present how squeezed cat states can increase bit flip suppression at no phase flip cost. Cat qubits typically suppress bit flips by mean of increasing the number of photons in the memory, which in exchange causes a linear increase of phase-flips. Squeezing limits bit flips while keeping phase flips constant. This makes for an easier and possibly earlier implementation of a repetition code below threshold and the construction of a high-fidelity logical qubit. 

Wednesday March 6, 03:48 pm – 04:00 pm, Room 200CD

Advances in Single Microwave Photon Detection 

By Alexandre May – Quantum Experimentalist

Alexandre will present our recent results in Circuit Quantum Electrodynamics (CQED). Detecting microwave photons is a formidable challenge due to the energy gap, approximately five orders of magnitude larger than optical photons, rendering semiconductor-based technologies ineffective. Our latest results extend superconducting-based concepts, substantially reducing detector noise, pushing the boundaries of detection capabilities. 

Wednesday March 6, 5:36 pm – 5:48 pm.  Room 201AB


Low-overhead quantum processor using concatenated bosonic-LDPC code 

By Diego Ruiz – Quantum Theorist

Diego will present a new quantum computing architecture encoding 100 high-fidelity logical qubits in 1500 cat qubits using LDPC codes. Cat qubits, thanks to their inherent protection against bit-flip errors, reduce quantum error correction to that of classical error correction. Whereas previous architectures proposed the use of a repetition code, we show that using LDPC codes allows for better performances while staying with a simple 2D local architecture. 

Thursday March 7, 3:24 pm – 3:36 pm, Room 200CD 


Analysis of DC voltage biased Josephson junctions for cat qubit stabilization 

By Thiziri Aissaoui – Quantum Theorist 

Thiziri will present a novel circuit proposal employing DC-biased Josephson junctions for implementing the necessary two-photon dissipation to stabilize cat qubits. Current cat qubit circuits rely on microwave pumps for implementing two-photon exchange, but larger pumps pose challenges. Our proposal eliminates the need for large pumps to effectively stabilize cat qubits. 

Friday March 8th, 10:48 am – 11:00 am, Room 200CD

Loss channel analysis of cat qubit circuits

By Léon Carde – Quantum Theorist

Léon will precisely model the processes that cause phase-flips in the dissipative cat qubit, using both analytical and numerical methods. This allows us to identify mitigation techniques for an improved cat-qubit operation.  

Friday March 8, 1:18 pm – 1:30 pm, Room 200CD 


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