Debasis Sadhukhan | LIP6 - Équipe QI

Restricted Randomized Benchmarking with Universal Gates of Fixed Sequence Length

Sun, 24 Nov 2024 00:00:00 +0000

The standard randomized benchmarking protocol requires access to often complex operations that are not always directly accessible. Compiler optimization does not always ensure equal sequence length of the directly accessible universal gates for each random operation. We introduce a version of the RB protocol that creates Haar-randomness using a directly accessible universal gate set of equal sequence length rather than relying upon a t-design or even an approximate one. This makes our protocol highly resource efficient and practical for small qubit numbers. We exemplify our protocol for creating Haar-randomness in the case of single and two qubits. Benchmarking our result with the standard RB protocol, allows us to calculate the overestimation of the average gate fidelity as compared to the standard technique. We augment our findings with a noise analysis which demonstrates that our method could be an effective tool for building accurate models of experimental noise.

Simplifying errors by symmetry and randomisation

Tue, 14 Nov 2023 00:00:00 +0000

We present a set of methods to generate less complex error channels by quantum circuit parallelisation. The resulting errors are simplified as a consequence of their symmetrisation and randomisation. Initially, the case of a single error channel is analysed; these results are then generalised to multiple error channels. Error simplification for each method is shown to be either constant, linear, or exponential in terms of system size. Finally, example applications are provided, along with experiments run on superconducting quantum hardware and numerical simulation. These applications are: (1) reducing the sample complexity of matrix-inversion measurement error mitigation by error symmetrisation, (2) improving the effectiveness of noise-estimation circuit error mitigation by error randomisation, and (3) improving the predictability of noisy circuit performance by error randomisation.

Shortcut to adiabaticity and sustainable entanglement in long-range quantum systems

Wed, 10 Nov 2021 16:00:00 +0100

Recent progress in various disciplines of physics has established our ability to control quantum effects in quantum devices and thus paving the way for promising near-future quantum technologies. Shortcut to adiabaticity is one of such techniques that can be used to suppress defects which arise due to the presence of a quantum critical point in between a quantum quench. In this talk I will be exploiting long-range systems for implementing shortcut to adiabaticity using an inhomogeneous quench. In the first part of the talk, I will focus on how to identify the critical to noncritical crossover in such long-range models just by looking at the correlation function and then show that it is possible to get a defect-free state only when the inhomogeneous front moves slower than a characteristic crossover velocity. In the second part, I will talk about scenarios where we can get sustainable entanglement at least over some reasonable duration when the system interacts with some noisy environment.