Periodic Reporting for period 1 - QUSON (Quantum Sensing with Quantum Optical Networks)
Reporting period: 2018-06-04 to 2020-06-03
Sensors play a key role in our modern society. They are an essential component in all kind of technologies, ranging from smartphones and cars to large-scale applications in industrial engineering. The new paradigm of quantum sensing is based on the idea of exploiting quantum effects, such as entanglement, to build measurement devices with greatly enhanced sensitivities. Prospective examples include clocks and sensors for applications in defence, gravity sensors for subsurface mapping in civil engineering, or quantum magnetometers for healthcare and diagnosis.
In the last decade we have witnessed a significant advance in experimental platforms such as trapped ion setups and superconducting circuits. These systems are never free from noise and dissipation, given that they need to couple to the external world that we want to measure. Unfortunately, the dissipation induced by the coupling to the environment has very detrimental effects for the generation of quantum states that can be used in metrology.
However, even in systems with strong dissipation, cooperative many-body effects may induce complex quantum dynamics, with emergent phenomena such as non-equilibrium phase transitions and multi-stability. The question then arises whether we can exploit those many-body effects in robust metrological protocols. In this project, we have investigated the potential to generate and harvest quantum correlations in dissipative many-body systems for its use in metrology. Our work has established several viable platforms where dissipation can become an asset rather than a liability, paving the way for a next generation of quantum sensors in dissipative environments.
In the last decade we have witnessed a significant advance in experimental platforms such as trapped ion setups and superconducting circuits. These systems are never free from noise and dissipation, given that they need to couple to the external world that we want to measure. Unfortunately, the dissipation induced by the coupling to the environment has very detrimental effects for the generation of quantum states that can be used in metrology.
However, even in systems with strong dissipation, cooperative many-body effects may induce complex quantum dynamics, with emergent phenomena such as non-equilibrium phase transitions and multi-stability. The question then arises whether we can exploit those many-body effects in robust metrological protocols. In this project, we have investigated the potential to generate and harvest quantum correlations in dissipative many-body systems for its use in metrology. Our work has established several viable platforms where dissipation can become an asset rather than a liability, paving the way for a next generation of quantum sensors in dissipative environments.
In general, our work has been devoted to investigate the emergence of quantum correlations of metrological interest in many-body systems that are in contact with the external environment.
First, we focused on the study of ensemble of atoms that are coupled to the environment in a collective way, meaning that atoms release the energy to the environment together, rather than individually. This behaviour can be achieved by using an optical cavity that acts as an intermediary of the interactions between the atoms and the environment. Notably, the coupling between the atoms and the cavity can be engineered by optical means, which allows to, in turn, engineer the dissipation towards the environment. We provided a systematic analysis of the stationary state achieved by the atomic ensemble when different types of engineered dissipation are compensated by an optical driving. This way, we identified regimes where the collection of atoms relax to a so-called “spin squeezed state”: a particular type of quantum state that provides enhanced sensitivity to external parameters, such as small electric fields.
In a second part of our project, we studied 1D networks of quantum systems that couple independently to the environment, also in an engineered way. We established a general set of conditions that, when satisfied, guarantee that the system will end up behaving like a quantum-entangled clock, i.e. displaying persistent oscillations underpinned by quantum entanglement and powered by dissipation (rather than prevented by it).
Further investigations in our project have analysed related problems in quantum metrology, such as the detection of quantum coherence in dissipative systems, or the reconstruction of quantum states from experimental data aided by neural-networks.
First, we focused on the study of ensemble of atoms that are coupled to the environment in a collective way, meaning that atoms release the energy to the environment together, rather than individually. This behaviour can be achieved by using an optical cavity that acts as an intermediary of the interactions between the atoms and the environment. Notably, the coupling between the atoms and the cavity can be engineered by optical means, which allows to, in turn, engineer the dissipation towards the environment. We provided a systematic analysis of the stationary state achieved by the atomic ensemble when different types of engineered dissipation are compensated by an optical driving. This way, we identified regimes where the collection of atoms relax to a so-called “spin squeezed state”: a particular type of quantum state that provides enhanced sensitivity to external parameters, such as small electric fields.
In a second part of our project, we studied 1D networks of quantum systems that couple independently to the environment, also in an engineered way. We established a general set of conditions that, when satisfied, guarantee that the system will end up behaving like a quantum-entangled clock, i.e. displaying persistent oscillations underpinned by quantum entanglement and powered by dissipation (rather than prevented by it).
Further investigations in our project have analysed related problems in quantum metrology, such as the detection of quantum coherence in dissipative systems, or the reconstruction of quantum states from experimental data aided by neural-networks.
Our work has established a solid body of theoretical understanding on the generation of quantum states for metrological applications in realistic systems coupled to an external environment, revealing viable research directions for the development of future experiments.
Our results represent a significant contribution to the development of quantum metrology in the European Union. This technology is expected to have a strong impact in key aspects of society such as healthcare, civil engineering, telecommunications or defence. In order to ensure this benefit, we have committed to the dissemination of our results through publications in high-impact peer-review journals (5 published at the end of the period, 3 in preparation), as well as in open repositories; presentations in conferences; academic visits to experimental groups and outreach activities for the general public.
Our results represent a significant contribution to the development of quantum metrology in the European Union. This technology is expected to have a strong impact in key aspects of society such as healthcare, civil engineering, telecommunications or defence. In order to ensure this benefit, we have committed to the dissemination of our results through publications in high-impact peer-review journals (5 published at the end of the period, 3 in preparation), as well as in open repositories; presentations in conferences; academic visits to experimental groups and outreach activities for the general public.