# Cryo Quantum Lab

In our laboratory we develop and investigate several types of ultrasensitive superconducting and micromechanical devices, with special interest in the application to quantum technologies and fundamental physics. We have available a large dry dilution refrigerator with base temperature 20 mK, equipped with microwave and SQUID instrumentation, a wet dilution refrigerator and several liquid helium cryostats.

## Superconducting quantum sensors and devices

We have recently started several projects in the field of superconducting quantum technologies. In particular, we are currently investigating superconducting quantum devices operated in the microwave domain, with focus on parametric amplifiers and single photon detectors.

**Josephson Parametric Amplifiers (JPA)**

We are developing flux-pumped Josephson Parametric Amplifiers (JPA), composed of coplanar resonators terminated by a double junction SQUID. We are interested in these devices because of their unique potential as ultralow noise amplifiers of microwave signals, capable of approaching the standard quantum limit (SQL) or even overcoming the SQL when operated in the degenerate phase-sensitive mode. Quantum limited amplification of microwave signals is needed in circuit-QED systems and quantum computing, but is also relevant in fundamental physics, for instance in the detection of axionlike dark matter. On a more fundamental level, the flux-pumped JPA is a paradigmatic system which allows one to observe the so-called Dynamical Casimir Effect (DCE), i.e. the generation of pairs of entangled photons out of the quantum vacuum. We aim at observing the DCE and characterizing some of its remarkable properties, including dissipative effects. This research is funded by Q@TN and by INFN (project Qub-IT), and is carried out in strict collaboration with FBK (B. Margesin) and CNR-INO (I. Carusotto).

**Traveling-wave parametric amplifiers (TWPA)**

We are partners of the INFN project DARTWARS, aiming at developing traveling-wave parametric amplifiers (TWPA) for broadband and general purpose amplification of microwave signals. In contrast with simple JPAs which are inherently narrowband, TWPAs can be designed as broadband amplifiers, with performance close to the quantum limit over a bandwidth of several GHz. In our group we develop TWPAs based on kinetic inductance nonlinearity, in collaboration with University of Milano Bicocca (A. Giachero) and FBK.

**Radiation Detectors**

We develop two different types of cryogenic radiation detectors based on superconducting devices:

SQUID-detected Transition Edge Sensors (TES) aiming at detecting single photons at ultralow energy (<100 GHz). The devices are developed in the context of the INFN project SIMP, in collaboration with INRIM in Turin (M. Rajteri group) and CNR-NEST in Pisa (F. Giazotto group).

Kinetic Inductance Detectors, based on microwave resonators with enhanced kinetic inductance. The devices are fabricated by FBK, in collaboration with University of Milano Bicocca (A. Giachero). We have demonstrated single photon resolution at telecom wavelength.

## Micromechanics and Quantum Foundations

We have a specific and unique expertise in the field of ultrasensitive detection of weak forces, by means of micromechanical devices cooled to ultralow temperature. We have pioneered a magnetomecanical detection method in which the motion of a microferromagnetic particle is detected by a ultralow noise SQUID. With this method we can measure the very tiny microcantilevers with high quality factor (Q>1E6) down to ultralow temperature (T<50 mK). Initially developed in the context of nanoMRI imaging techniques, this detection method allows to achieve extreme force sensitivity, enabling interesting applications in the context of fundamental physics.

As main recent achievement, we have performed some of the most stringent *tests of wave function spontaneous collapse models*, in particular of the most known of these models, the so-called Continuous Spontaneous Localization (CSL). Collapse models have been proposed as a possible solution of the interpretive problems of quantum mechanics, by assuming that the collapse of the wave function is a real effect. In collapse models, the unitary evolution of a quantum system is complemented by a universal mass-proportional dynamical localization mechanism (= collapse in space), encoded by stochastic and nonlinear modifications of the Schrodinger equation. As simplest prediction, this collapse dynamics suppresses quantum superpositions of a massive objects, in contrast with atomic and molecular systems, where superposition states can be observed. However, a common and unavoidable side effect of collapse models is a tiny violation of the energy conservation principle, which can be searched for by means of sensitive mechanical mesurement. By accurately monitoring the motion of an ultraisolated microcantilever at millikelvin temperature, we have indeed set the *strongest unambiguous bound on the CSL model to date*.

This research is carried out in collaboration with several international partners, in particular Hendrik Ulbricht (University of Southampton), Angelo Bassi (University of Trieste), Tjerk Oosterkamp (University of Leiden).

## Levitated magnetomechanics

We have recently managed to manipulate *magnetically levitated micromagnets* using a superconducting trap, demonstrating their unique potential as mechanical systems with even lower dissipation. In particular, we have proposed several original schemes for ultrasensitive measurements, which include *tests of collap**se models*, the observation of *Larmor precession* in a macroscopic magnet and the realization of *magnetometers and torque sensors with unprecedented resolution*.

We are coordinators of the EU project LEMAQUME (LEvitated MAgnets for QUantum MEtrology), recently funded within the QuantERA Call 2021. The project aims at realizing levitated micromagnets over several different platforms and demonstrate the potential to realize ultrasensitive magnetometers and torque sensors. The project will be carried out by a world class consortium, with main partners from Germany, France, Israel and Latvia, and external partners from UK and US.

In Trento we will develop a levitation platform based on hard micromagnets floated in superconducting traps in the Meissner state. We aim at demonstrating the potential of these systems as ultrasensitive magnetometers with sensitivity well beyond the Energy Resolution Limit and exploring the interplay between precessional and librational dynamics. Furthermore, we plan to perform fifth-force measurements, aiming at exploring the parameter space of exotic spin-spin interaction models.

## Gravitational wave detection in space

We collaborate to the development of the LISA space-based gravitational wave detector. A member of our group (A. Cavalleri) is part of the *LISA team in Trento*, which is developing and characterizing the inertial sensor. The main goal of current activity is the study of the charge-induced electrostatic forces exerted on free-falling test masses.