Home-built three-stage dual optical parametric amplifier system for generating highly tunable pulses in the mid-infrared and terahertz spectral ranges.
Research vision
In distinct classes of many-body systems, quantum coherence and entanglement persist across macroscopic length scales and a broad range of temperatures. This phenomenon is particularly evident in collective behaviors such as superconductivity, strange metallicity, or topologically ordered phases. However, the experimental validation and precise quantification of quantum correlations and entanglement in systems comprising a macroscopic (Avogadro) number of particles and degrees of freedom represents a current challenge.
In our group, we plan to address this question with the tools of ultrafast light-matter interactions. We develop the spectroscopic and theoretical methodologies to detect, isolate, and characterize quantum coherence on macroscopic scales. Additionally, we use techniques from non-equilibrium physics to engineer novel quantum phases that are beyond the reach of traditional thermodynamic pathways.
Sub-cycle quantum dynamics driven by non-Poissonian fields
We study how the photon statistics of the electromagnetic field leave an imprint on the dynamics of collective excitations and quasiparticles in solids (e.g., electrons, excitons, magnons, phonons etc). One central question is: which features of the light–matter interaction in solids depend on the field statistics beyond the mean intensity? Can weak transitions be enhanced, which non-equilibrium states can be realized, and which sub-cycle interferences appear that are absent under coherent excitation when driving matter with non-Poissonian (incl. “non-classical”) light? Experimentally, we use and develop bright sources of non-Poissonian ultrafast light and combine them with phase -stable intense mid-infrared and terahertz transients to reach new regimes of nonlinear light matter interaction driven by tailored sub-cycle fluctuations. In parallel, we develop new shot-resolved detection schemes based on photon-correlation measurements, conditioning, heralding, and quantum tomography. The ultimate goal is to address fundamental problems related to the emergence of macroscopic coherence in solids and its control — for example, the realization of light-induced excitonic condensation, isolating dark or multi-quantum excitations, and identifying signatures of pairing fluctuations above the superconducting transition.
Non-classical states of matter excitations
Most of the time, ultrafast pump-probe spectroscopy prepares macroscopic ensembles of matter excitations: a coherent pulse resonant with a phonon mode launches a coherent state of that mode containing many quanta, and the detected signal averages over this ensemble. Isolating a single quantum of a collective mode, such as an individual phonon Fock state, or a single magnon, and preparing it in a non-classical state is a highly non-trivial task. Our vision is the preparation of magnons, phonons, and excitons in non-classical quantum states — squeezed, Fock, and non-Gaussian superpositions — by employing conditioning and post selection techniques inspired by related fields sic as quantum optics and quantum optomechanics. The scientific motivation is twofold: such states enable spectroscopy of the host material with sensitivity beyond the standard quantum limit, and they are themselves can be used as local inherent sensors which can be used to study the quantum-classical boundary in macroscopic, strongly interacting solids.
Ultrafast terahertz microscopy of low-dimensional materials
We are building a terahertz pump–terahertz probe microscope with sub-wavelength spatial resolution and single-shot electro-optical sampling readout. The microscope is designed for low-temperature measurements on exfoliated and gated two-dimensional devices. The latter have largely eluded investigation in the terahertz range due the mismatch between the focal size of diffraction-limited terahertz radiation and the lateral size of a typical device. Our microscope will enable two-dimensional terahertz spectroscopy, realization of Floquet dressing and broadband time-resolved conductivity, in correlated stacked van der Waals systems.
Ultrafast quantum sensing
We combine femtosecond optical pulses with microwave control sequences to manipulate point defect quantum sensors such as NV centers in diamond. The central ambition is to bridge the time-scale gap between optical pump experiments (femtoseconds to picoseconds) and standard NV protocols (nanoseconds and longer) in order to track ultrafast magnetic dynamics with high spatial and temporal resolution.