Substrate-transferred crystalline coatings are a groundbreaking new concept for the fabrication of ultralow-loss mirrors. The single-crystal lattice structure of these substrate-transferred GaAs/AlGaAs Bragg mirrors exhibits the lowest mechanical losses and hence unmatched Brownian noise performance, which nowadays limits the stability of precision optical interferometers. Another outstanding feature of these coatings is the wide spectral coverage of the GaAs/AlGaAs material platform. Limited by interband absorption at short wavelengths and the reststrahlen band at long wavelengths, crystalline coatings can be employed as low-loss multilayers from approximately 900 nm up to 5 μm and beyond. Excellent optical performance has been demonstrated in the near-infrared with excess optical losses (scatter + absorption) as low as 3 parts per million (ppm), enabling cavity finesse values up to 360,000 at 1.55 μm. Our first attempts at applying crystalline coatings in the mid-infrared has resulted in mirrors with excess optical losses of 159 and 242 ppm at 3.3 and 3.7 μm, respectively. Remarkably, these results are already on par with current state-of-the-art amorphous mirror coatings. Absorption measurements based on photothermal common-path interferometry (PCI) reveal that the optical losses are largely dominated by optical scatter. Via, PCI, we have confirmed absorption losses below 10 ppm at 3.7 μm, showing the enormous potential of GaAs/AlGaAs Bragg mirrors at mid-infrared wavelengths. An optimized fabrication process, which is currently under development, can efficiently suppress optical scatter due to accumulated growth defects on the surface. Ultimately, we foresee excess losses significantly less than 50 ppm in the mid-infrared spectral region.
Substrate-transferred crystalline coatings have recently emerged as a groundbreaking new concept in optical
interference coatings. Building upon our initial demonstration of this technology, we have recently realized significant
improvements in the limiting optical performance of these novel single-crystal GaAs/AlGaAs multilayers. In the nearinfrared
(NIR), for center wavelengths spanning 1064 to 1560 nm, we have reduced the excess optical losses (scatter +
absorption) to less than 5 ppm, enabling the realization of a cavity finesse exceeding 300,000 at the telecom-relevant
wavelength range near 1550 nm. Moreover, we demonstrate the direct measurement of sub-ppm optical absorption at
1064 nm. Concurrently, we investigate the mid-IR (MIR) properties of these coatings and observe exceptional
performance for first attempts in this important wavelength region. Specifically, we verify excess losses at the hundred
ppm level for wavelengths of 3300 and 3700 nm. Taken together, our NIR optical losses are now fully competitive with
ion beam sputtered films, while our first prototype MIR optics have already reached state-of-the-art performance levels
for reflectors covering the important fingerprint region for optical gas sensing. Thus, mirrors fabricated via this
technique exhibit the lowest mechanical loss (and thus Brownian noise), the highest thermal conductivity, and,
potentially, the widest spectral coverage of any “supermirror” technology, owing to state-of-the art levels of scatter and
absorption losses in both the near and mid IR, all in a single material platform. Looking ahead, we see a bright future for
crystalline coatings in applications requiring the ultimate levels of optical, thermal, and optomechanical performance.
Combining optical levitation and cavity optomechanics constitutes a promising approach to prepare and control the motional quantum state of massive objects (>10^9 amu). This, in turn, would represent a completely new type of light-matter interface and has, for example, been predicted to enable experimental tests of macrorealistic models or of non-Newtonian gravity at small length scales. Such ideas have triggered significant experimental efforts to realizing such novel systems.
To this end, we have recently successfully demonstrated cavity-cooling of a levitated sub-micron silica particle in a classical regime at a pressure of approximately 1mbar. Access to higher vacuum of approx. 10^-6 mbar has been demonstrated using 3D-feedback cooling in optical tweezers without cavity-coupling.
Here we will illustrate our strategy towards trapping, 3D-cooling and quantum control of nanoparticles in ultra-high vacuum using cavity-based feedback cooling methods and clean particle loading with hollow-core photonic crystal fibers. We will also discuss the current experimental progress both in 3D-cavity cooling and HCPCF-based transport of nanoparticles.
As yet another application of cavity-controlled levitated nanoparticles we will show how to implement a thermodynamic Sterling cycle operating in the underdamped regime. We present optimized protocols with respect to efficiency at maximum power in this little explored regime. We also show that the excellent level of control in our system will allow reproducing all relevant features of such optimized protocols. In a next step, this will enable studies of thermodynamics cycles in a regime where the quantization of the mechanical motion becomes relevant.
Quantum metrology utilizes nonclassical states (of light) to
outperform the accuracy limits of its classical counterpart. We
demonstrate the relevance of photon number Fock states and
polarization entanglement for the experimental realization of
interferometric quantum metrology applications.
We have tested the experimental prerequisites for a Space-to-Ground quantum communication link between satellites and an optical ground station. The feasibility of our ideas is being tested using the facilities of the ASI Matera Laser Ranging Observatory (MLRO) and existing geodetic satellites such as Lageos 1 and 2. Specific emphasis is put on the necessary technological modifications of the existing infrastructure to achieve single photon reception from an orbiting satellite.
Quantum physics experiments in space using entangled photons and
satellites are within reach of current technology. We propose a series of fundamental quantum physics experiments that make advantageous use of the space infrastructure with specific emphasis on the satellite-based distribution of entangled photon pairs. The experiments are feasible already today and will eventually lead to a Bell-experiment over thousands of kilometers, thus demonstrating quantum correlations over distances which cannot be achieved by purely earth-bound experiments.