Research

Description of main themes:

Project is divided into three main thrusts:

1. Development of non-classical sources of light in the MIR Quantum sources of light lie at the heart of all quantum spectroscopy techniques. As is common in the visible, and following some of our previous work, parametric processes will be employed as the primary source of squeezed MIR light. However, to reap the greatest quantum advantage, we will work in the time domain. Indeed, pulsed lasers establish the most natural time base for quantum metrology and will serve as the classical pump in all of our schemes, while also allowing for additional discrimination against the thermal background. This strategy will allow for identical state preparation and time-tagging at event rates as high as 106-109 per second. In addition, stabilized pulsed lasers, also called frequency combs for their applications in precision metrology, enable the preparation of phase-locked pulses where the optical waveform under the ultrashort envelope remains identical from one realization to the next. Together with high peak powers, frequency combs form ideal sources for quantum nonlinear photonics. Frequency combs with quantum output will be demonstrated in MIR.

At the same time, quantum-correlated photon pairs and entangled photon-number quantum states are one of the enabling building blocks for next-generation metrology and quantum sensing applications. Besides entanglement, such sources offer the possibility to realize interferometers that operate at ultra-low light levels in which quantum interference provides unmatched sub-shot-noise sensitivity compared to classical counterparts. At present, bright single-photon emitters are a mature technology in the visible and telecommunications wavelengths and Si-based quantum photonic circuits can implement combined single-photon states with intensity-symmetric multiport beam splitters for high efficiency entangled N00N state generation. ingle-photon states also become a resource when combined with other quantum states, e.g. holding great promise for spectroscopy when entangled pair-wise or when combined with squeezed states, which can produceg exotic outputs such as Schrödinger cat states that show Wigner negativity. Yet, MIR quantum sources are surprisingly lagging behind and none can rival with visible and NIR sources in terms of brightness, single-photon purity, and indistinguishability. Se will work towards realizing the first “on-demand” sources of single photons in the MIR, such as those based on single emitters in high-purity Ge and GaAs material platforms and on single-photon nonlinearities in the strong coupling regime.

2. Quantum detectors of MIR nonclassical light Because of the poor noise characteristics inherent to conventional MIR photodetectors (e.g. HgCdTe, DLaTGS, InSb), sensitive light detection in this spectral range poses many challenges. However, newly developed ultrafast techniques also allow for unique opportunities specific to the MIR. The possibility of electro-optic sampling of the electric field is ideal for quantum measurement and has already been explored by our team for sensing quantum vacuum fluctuations. Thermal background noise from the sample itself also poses an important challenge, but this can be circumvented to some degree via our time-resolved approach. Doing this effectively will require the development of fast detectors with outstanding noise characteristics. For this, we plan to develop >10 GHz bandwidth (high repetition rate) MIR SPADs operating at modest (liquid nitrogen) temperatures.

3. Chip-integrated photonics for sensing Integrated components are disareable from both a systems and a performance perspective. Integrated components allow for scalability, low-loss, efficient coupling to analytes (increased sensitivity), simple thermal management and the realization of resonators and nonlinear elements that would not be possible off-chip. For high optical bandwidth measurements, frequency-comb-driven quantum sources will be delivered on-chip via an optical fiber, while for targeted detection of specific resonances of an analyte, frequency combs based on QCLs can be used and directly heterointegration as demonstrated by our team. Within this program, we will design optimized linear and nonlinear waveguides, couplers and resonators for on-chip integration using LiNbO3 and Ge-on-Si material platforms, both compatible with MIR integrated photonic applications. As proof-of-concept demonstrations for on- chip sensing, we will target greenhouse gases such as CO2 or N2O (which can be detected within the 3 μm transparency window of water) and molecules sharing bonds that are also relevant for defense applications (such as C=O in TATP explosives, in the 8-12 μm range, or C-Cl in sulfur mustard, in the 6-12 μm range).