A PhD position is available in our group at the University of Valencia / IFIC-CSIC. The thesis will be centered on the topics of quantum information theory, geometry and quantum machine learning. 

The position is funded by the European Network CaLiForNIA through a Marie Skłodowska-Curie Action. It will be co-supervised in collaboration with the University of Bologna. For more information about the position and details on the application: https://euraxess.ec.europa.eu/jobs/195173 

Quantum metrology provides the theory foundation for deriving the quantum limits on the estimation of any parameter of a quantum system. Over the past decades, this theory has been successfully applied to a wide range of scenarios, with the focus lying mostly on interferometric measurements, where the parameter is treated as a parameter of a quantum state that is defined on a fixed set of modes. Optical modes contain information about the position, time, frequency and polarization of the light field. Extracting these parameters therefore requires a quantum metrology theory for mode parameters. In this work, we develop such a theory and derive the quantum limits on mode parameter estimation. We find recipes that allow for quantum-enhanced precision in the estimation of any such mode parameter through the population of suitable modes with suitable nonclassical states. This opens up new avenues for spectroscopy, positioning, timing, and superresolution imaging beyond the classical limit.

M. Gessner, N. Treps, and C. Fabre, Optica 10, 996 (2023).

The quantum Cramér-Rao bound is the cornerstone of modern quantum metrology theory. It is derived from the classical Cramér-Rao bound by optimizing over the choice of the quantum measurement. Despite its widespread use, this bound has some known shortcomings. For example, it tends to overestimate the achievable sensitivity from a small data sample, and it poses strict regularity conditions that may not be fulfilled by all data samples. In this work, we derive a family of generalized sensitivity bounds for quantum metrology that allow us to avoid these limitations. We obtain an entire hierarchy of bounds by optimizing the choice of measurement in families of classical bounds that include the Cramér-Rao bound at the lowest order. Our generalized bounds generally provide larger error bounds that converge towards the Cramér-Rao bound in the limit of large data samples and when the system is prepared in a pure state.

M. Gessner and A. Smerzi, Phys. Rev. Lett. 130, 260801 (2023).

We have a PostDoc opening available at IFIC (University of Valencia and CSIC). The candidate would work in our research group that includes researchers from the Theoretical Physics Department of the University Valencia and IFIC (Prof. Armando Perez and Dr. Manuel Gessner), which is a joint University-CSIC institute, as well as collaborators from the Technical University of Valencia (Dr. Carmen G. Almudever and Dr. M.A. Garcia-March). The duration of the postdoc position will be two years, with the option to extend it to one more year. The goals of the project cover a variety of aspects related to quantum computers, quantum simulation of many-body theories, quantum metrology or quantum machine learning, although expertise on other areas of quantum information and quantum technologies will also be evaluated.

https://quantiki.org/position/postdoc-position-university-valencia-spain

Testing quantum mechanics with 16-microgram Schrödinger cat states

The superposition principle is one of the most fundamental principles of quantum mechanics. According to the Schrödinger equation, a physical system can be in any linear combination of its possible states. Although the validity of this principle is routinely confirmed for microscopic systems, it remains unclear why macroscopic objects are not observed to be in superpositions of distinguishable states. Our experiments demonstrate the preparation of a mechanical resonator with an effective mass of 16 micrograms in nonclassical states of motion, such as Fock states and Schrödinger cat states. Furthermore, we investigate the decoherence dynamics of these states by observing the disappearance of Wigner negativities, which allows us to derive constraints on possible modifications to the Schrödinger equation. Our results have potential applications in continuous variable quantum information processing, quantum sensing, and in the fundamental investigation of quantum mechanics on massive systems.

References:

”Macroscopic Quantum Test with Bulk Acoustic Wave Resonators”

Björn Schrinski, Yu Yang, Uwe von Lüpke, Marius Bild, Yiwen Chu, Klaus Hornberger, Stefan Nimmrichter, and Matteo Fadel

Phys. Rev. Lett. 130, 133604 (2023)

“Schrödinger cat states of a 16-microgram mechanical oscillator”

Marius Bild, Matteo Fadel, Yu Yang, Uwe von Lüpke, Phillip Martin, Alessandro Bruno, and Yiwen Chu

Science 380, 274 (2023)

The Societat Catalana de Física has awarded Pau Colomer the Accèssit (2nd price) of the Premi Jordi Porta i Jué for his Master's thesis "Quantum-enhanced estimation of a mode parameter". Congratulations!