Giacomo Marocco

Welcome! I’m a postdoctoral researcher in the Physics Division at Berkeley Lab. I work to understand the quantum mechanics of the devices that we are building to discover new fundamental physics. This often involves a fun blend of quantum measurement theory, quantum optics, and particle theory. I am doing this in the Quantum Measurements group, run by Dan Carney.

Links and contact

Research

Many quantum experiments are being built in the effort to discover new physics. I like to make sure that these quantum systems work well by modelling them and coming up with new architectures and sensing protocols. I’m currently most interested in optical and superconducting systems.

Previously, I spent a lot of time doing theoretical particle physics: searching for new particles in old experimental data, and conceptualising new experiments.

Projects

Quantum optomechanics

Teams at Berkeley Lab and Yale are developing a levitated nanoparticle platform to search for sterile neutrinos, called the Quantum Invisible Particle Sensor (QuIPS). I have worked on developing quantum-enhanced protocols to increase the sensitivity of this optomechanical system. One can use squeezed light to do this; alternatively, I have shown that one can directly squeeze the motional state of the particle, which is the first practical procedure that increases the sensitivity to signals along arbitrary directions. I sometimes put forward new kinds of measurements this device can make to learn about nuclear physics.

I have also developed a new scheme to measure forces at the standard quantum limit in the kHz to MHz frequency band with levitated superconductors. This involves using a flux-tunable microwave resonator to readout the position of the superconducting sphere, which enables the detection of high-frequency gravitational waves. These superconducting systems are currently being constructed by Prof. Gerard Higgins at the Austrian Academy of Sciences.

Many other kinds of optomechanical sensors are being built to search for dark matter, for instance micro-electromechanical systems. These are often read out optically, with the aim of measuring the interaction of dark matter with these devices at the standard quantum limit. I have shown how optical heating in these systems can be mitigated with squeezed light, which allows larger arrays of these sensors to operate in dilution fridges with limited cooling capacity.

Solid-state excitations

Recent advances in superconducting sensors have enabled the detection of low-energy, collective excitations in solid-state materials, such as phonons (vibrational waves) and magnons (spin waves). I am interested in both understanding how dark matter may be detected via this signal and designing new schemes to detect these excitations in a scalable way. I have calculated how axions convert to phonons in various materials, and how other dark matter candidates create magnons in scattering off magnetically ordered materials, particularly quasi-two-dimensional magnets. More recently, I have worked on detecting dark photons through their vibrational signature in amorphous materials with arrays of transition edge sensors.

High-intensity laser experiments

During my PhD, I spent time designing ways of looking for axions with high-intensity lasers. These axions are hypothetical new particles that interact with the electromagnetic field, and so might show up in settings with a large density of electromagnetic radiation. This work culminated in an experiment we did at the High Energy Density facility at the European XFEL. We set limits on axion production and reconversion in the coherent interaction of the X-ray beam with a pair of aligned germanium crystals.