Probing and verifying large-scale quantum technologies via randomized measurements – QRand

There is a strong ongoing effort in developing quantum technologies made of cold atoms, superconducting qubits, etc. These experimental platforms can be used to build quantum simulators, which are systems of artificial quantum matter that can emulate the many-body physics of key quantum phenomena (high-temperature superconductivity, topological phases, etc). An important prospect for these systems is also the design and fabrication of quantum computers made of « quantum bits », which can outperform classical computers, and in particular solve hard optimization problems.
While there is significant investment in quantum technologies, there is a still a major challenge that deserves attention: How to measure in an experiment the key quantities that describe many-body quantum systems, such as entanglement?

The QRand project aims at addressing this challenge by proposing a universal measurement toolbox for quantum technologies based on randomized measurements (RM). RM consist in applying random unitary operations to a quantum state before performing measurements. The statistical correlations between these measurements give then access to physical quantities of interest. The project investigator Benoit Vermersch (BV, maître de conférences University Grenoble Alpes) has developed these protocols during his postdoctoral employment, and has been involved in the first experimental demonstrations of RM that led to the first direct measurement of entanglement entropies in a trapped ion system. These first results have shown that randomized measurements can be in the future the method of reference to probe large scale quantum simulators and quantum computers.

The QRand project consists in two objectives:
The first goal of QRand is to derive a general theory for randomized measurements mapping the different physical quantities associated with a quantum state (which we would would like in the end to measure) to a combination of statistical moments of RM (which are the experimentally accessible quantities).
We expect high impact results for this theory: Our new RM protocols will allow to access in various experiments, for the first time, all entanglement Rényi entropies, the von-Neumann entropy, entanglement negativities quantifying universal properties of quantum phase transition at finite temperature, and the non-local order parameters that describe two-dimensional many-body topological phases.

Our second objective is to extend the range of setups where RM can be physically implemented. First, we will adapt and apply in two theory-experiment collaborations RM prototols in superconducting qubit quantum computers and quantum simulators. We will also develop ideas to physically implement for the first time RM with Rydberg atoms, and ultracold atoms implementing Hubbard models.
Our second objective will allow to routinely probe entanglement in various experimental platforms implementing large-scale quantum systems, and in particular to implement the new protocols that relate to our first objective.

QRand's ambitious research goals are supported by a unique methodology that combines quantum optics theory, random matrix theory and large-scale tensor-network numerical simulations. This interdisciplinary approach gives us the complete expertise that is required to propose measurement protocols for probing highly entangled states of many-body quantum matter with state-of-the-art quantum technology.

This project is a significant opportunity for BV to establish an independent research activity in quantum technologies theory in Grenoble, and to create strong synergies with local and international partners. The project benefits from strong collaboration agreements with experimental groups and with an industrial partner, who will apply existing and to be-developed RM protocols in their setups.