QLM Technology is developing a new type of low-cost gas camera based on high-speed infrared single-photon avalanche detectors or SPADS. Our first target product is a methane imager that can accurately and continuously measure industrial natural gas emissions. We are currently completing integrated and industry-ready versions for our prospective customers to evaluate in early 2021. This talk will detail our imager design and present recent performance results in leak detection and other industrial metrology applications.
Quantum optical information systems offer the potential for secure communication and fast quantum computation. To fully characterise a quantum optical system one has to use quantum tomography.1 The integration of quantum optics onto photonic chips provides advantages such as miniaturisation and stability, significantly improving quantum tomography using both re-configurable, and more recently, simpler static designs. These on-chip designs have, so far, only used probabilistic single photon sources. Here we are working towards quantum tomography using a true deterministic source - an InGaAs quantum dot.
Latest advances in integrated single-photon detectors offer possibilities for gaining information inside quantum photonic circuits. We introduce a concept and provide experimental evidence for the inline tomographic mea- surement of multiphoton quantum states, while keeping the transmitted ones undisturbed. We establish that by recording photon correlations from optimally positioned detectors on top of coupled waveguides with de- tuned propagation constants, one can perform robust reconstruction of multiphoton density matrices describing the amplitude, phase, coherence and quantum entanglement. We report proof-of-principle experiments. Our method opens a pathway towards practical and fast inline state tomography for diverse applications in quantum photonics.
The processing of information encoded in frequency combs or spectral lattices has multiple applications for both classical and quantum states of light ranging from communications to spectroscopy. There is a strong interest in all-optical approaches for ultra-fast processing on integrated platforms. Here, we develop a concept and demonstrate experimentally all-optical flexible spectral comb reshaping in a nonlinear waveguide for two novel applications. First, we reveal that the evolution of an optical spectral comb can emulate wave dynamics in multi-dimensional lattices, which is a nontrivial generalization of previous theoretical proposals. In our experiment, a discrete signal spectrum is modulated by stronger pumps co-propagating in a nonlinear fiber with Kerr-type nonlinearity. Four-wave mixing Bragg scattering then induces coupling between many spectral lines, including nonlocal couplings between spectral lines which are further apart. We find that such a configuration can be exactly mapped to wave dynamics in complex multi-dimensional lattices, and as a representative example we realize a tube of triangular lattice. Importantly, the nontrivial phase of complex-valued couplings can give rise to synthetic gauge fields, and we directly measure corresponding asymmetric spectral reshaping. Our approach is scalable to higher-dimensional synthetic lattices. Second, we show that such a lattice with nonlocal couplings can enable the full reconstruction of the input spectra, including information on the phase and coherence, with a single-shot spectral intensity measurement. We demonstrate the reconstruction of input states composed of four frequency channels. Remarkably, the coherent nature of nonlinearly induced couplings is applicable for quantum states with spectral encoding.
With recent advances in nanophotonics, metasurfaces based on nano-resonators have facilitated novel types of optical devices. In particular, the interplay between different degrees of freedom, involving polarization and spatial modes, boosted classical polarization measurements and imaging applications. However, the use of metasurfaces for measuring the quantum states of light remains largely unexplored. Conventionally, the task of quantum state tomography is realized with several bulk optical elements, which need to be reconfigured multiple times. Such setups can suffer from decoherence, and there is a fundamental and practical interest in developing integrated solutions for measurement of multi-photon quantum states. We present a new concept and the first experimental realization of all-dielectric metasurfaces with no tuneable elements for imaging-based reconstruction of the full quantum state of entangled photons. Most prominently, we implement multi-photon interferometric measurements on a sub-wavelength thin optical element, which delivers ultimate miniaturization and extremely high robustness. Specifically, we realize a highly transparent all-dielectric metasurface, which spatially splits different components of quantum-polarization states. Then, a simple one-shot measurement of correlations with polarization-insensitive on-off click detectors enables complete reconstruction of multi-photon density matrices with high precision. In our experiment, we prepare sets of polarization states and reconstruct their density matrices with a high fidelity of over 99% for single photon states and above 95% for two-photon states. Our work provides a fundamental advance in the imaging of quantum states, where multi-photon quantum interference takes place at sub-wavelength scale.
Optical coherence is of fundamental importance for both classical and quantum applications. This motivates the development of approaches for increasing the degree of coherence, which can be quantified by a measure of purity. The purity is preserved in linear conservative systems, and accordingly the manipulation of coherence was realized with specially introduced loss in bulk optical setups or diffraction on metal films involving optical absorption and plasmon coupling. Here we suggest and show experimentally for the first time that manipulation and measurement of optical coherence and state purification can be efficiently realized in integrated non-Hermitian parity-time (PT) symmetric photonic structures composed of elements with different loss or gain. Specifically, we design and fabricate laser-written waveguide directional couplers that contain two sections. The first section realizes a PT-like coupler, where one of the two waveguides features extra radiative losses via modulation. The second section consists of straight coupled waveguides with specially detuned propagation constants, which are optimized to enable a full reconstruction of the purity and optical coherence by measuring the interference pattern in both waveguides through fluorescence imaging. In PT symmetric regime, we observe that the purity of an initially fully incoherent (mixed) state is increased followed by a revival of the input state. This constitutes an important experimental evidence of reversible manipulation of light coherence in PT coupled waveguides. We anticipate that this method can facilitate a wide range of applications from classical to quantum optics, including filtering out noise and optimizing the visibility of interferometric measurements.
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