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All Solid-State Super-Twinning Photon Microscope

Periodic Reporting for period 1 - SUPERTWIN (All Solid-State Super-Twinning Photon Microscope)

Reporting period: 2016-03-01 to 2017-02-28

SUPERTWIN's prime objective is to develop the prototype of a new microscope that exploits entangled photons to overcome the resolution limit of classical optics, at half the photon wavelength lambda/2, being lambda the wavelength of the probing light. The SUPERTWIN microscope comprises three main building blocks: (i) solid-state emitters based on advanced group-III nitride and III-V alloy epitaxial growths and wafer processing techniques to generate highly entangled photon states; (ii) CMOS single-photon detector arrays with on chip pre-processing to record spatio-temporal multi-photon interference patterns; and (iii) dedicated data processing algorithms aimed at extracting the image of the illuminated object from the statistics of scattered entangled photons. The expected achievable resolution in this case is given by lambda/2N, where N is the degree of entanglement. SUPERTWIN concept will pave the way for a new paradigm in optical imaging, triggering the development of novel microscopy systems that will surpass existing super-resolution microscopy techniques. The long-term impact of SUPERTWIN technology will be in the market of optical and scanning probe microscopy as the method is based only on the scattering properties of the specimen surface SUPERTWIN, thus enabling a multitude of applications in biology, inspection and micro/nano technology. Last but not least, a number of side results are expected from the development of SUPERTWIN building blocks, impacting on different application fields ranging from quantum optics to industrial and biomedical.
A model experiment was developed to be used as a basis for the image extraction algorithm activity. An experiment was set-up relying on a well established source of entangled photons. Two types of detectors have been used: (i) a pair of movable single pixel detectors in the form of two optical fibers fixed on motorized stages and (ii) a multi-pixel based detection array to measure a second-order correlation function of entangled photons. This second experiment was crucial for the definition of the specifications and the design of the CMOS-SPAD array detectors.
Moreover, these experiments allowed for first results of a near-field quantum imaging experiment using double slits of various dimensions as objects. Eventually, an image reconstruction algorithm was developed and tested, demonstrating super-resolving regime.
As the illumination source targeted within SUPERTWIN will operate in the regime of superradiant (SR) emission, a study was performed to understand the possibility of field entanglement during SR emission form a continuous medium. Photon entanglement has been predicted to occur at the lowering edge of SR pulse.
A moltitude of semiconductor heterostructures on GaAs substrate for emission at 780nm or below have been designed. Three different Quantum Wells (QW) thicknesses have been implemented combined with three different numbers of QW. Extensive modelling was performed to investigate the main parameters, such as the band structure, gain spectra, optics waveguide, field with its confinement factors and transport and eventually extracting the internal parameters: internal quantum efficiency, internal losses, modal gain coefficient, etc., resulting in the list of geometries and composition of QWs for the fabrication of InGaN and GaAsP SUPERTWIN sources.
Regarding the InGaN-based sources, a laser structure consisting of 3xInGaN/GaN QWs was designed and manufactured. After processing, the laser bar was tested showing the expected behaviour with an emission wavelength at 433 nm.
Setups and verification procedures have been identified and mounted for the testing and validation of SUPERTWIN solid-state sources of entangled photons. They include (i) classical ultrafast pulse characterization, (ii) HBT correlation and (iii) HOM interferometric autocorrelation.
A first CMOS chip was designed and manufactured in a CMOS 150nm process, including three 32x32-pixel arrays based on three pixel architectures: two based on the timestamp concept, while the third architecture targets sub-ns validation of coincident photon events across the whole array. In addition, the consortium decided to investigate the suitability of the advanced 110nm CMOS Image Sensor technology node, in which no single-photon iamger has been demonstrated yet.
Methodologies for the validation of SUPERTWIN CMOS-SPAD detectors have been developed. The idea is to use sources of correlated light with well-established theoretical and experimental knowledge of their spatio-temporal correlations such as pseudo-thermal light sources and entangled 4-photon states produced in SPDC.
Two nanowire-SSPD array detectors with the capability of resolving the number of photons in an optical pulse up to 4 photons have been designed and manufactured. A system demonstrator was developed and validated experimentally.
Finally, an analysis of the end-user and market demands has been performed taking into account the ideal image resolution, acquisition time and SNR for a state-of-the-art microscope.
Some of the scientific results achieved from SUPERTWIN project consortium within the first year, set relevant progress beyond the state of the art in different disciplines.
Image Sensors/ SPAD-sensors (achieved):
- Use of CMOS single photon detector arrays in quantum imaging experiments. They will advantageously replace expensive intensified CCD.
- Development of pixel architectures optimized for quantum optics applications (high sensitivity, low crosstalk and highly-resolved time coincidence over large number of pixels).
Image Sensors/ SPAD-sensors (expected):
- Development of SPAD devices in CMOS technology with high sensitivity in the near infra-red region and low crosstalk (test structures are currently under test).
- Development of SPAD devices and CMOS-SPAD sensors in CMOS 110nm technology (test structures are currently under fabrication).
Quantum Physics/Optics (achieved):
- Development of a post semiclassical TLS model. Design of SUPERTWIN illumination source. Assembly of HOM setup for original phase- eraser with no moving parts testing pulse width and non-classicality of light states. Demonstration of single-shot g(2) measurements in HBT setup using oscilloscope in real time mode.
Quantum Physics/Optics (expected):
- Design of SUPERTWIN solid-state illumination source (experimental validation is ongoing).
- Optimization of the quantum antenna model for the shaping of the correlation functions of the emitted field (to be validated experimentally with the illumination source).
- Achievement of super-resolution with super-radiance by measuring the second-order correlation function.

Expected Impact of SUPERTWIN project:
- SUPERTWIN should be able to address the open issues where other imaging instruments fall short while not falling behind the state of the art possibilities.
- An Application and Exploitation Advisory Board has been set up; AEAB members suggested interesting side impact possibilities originated by the development of SUPERTWIN CMOS-SPAD sensor:
- NIR-sensitive, low cross-talk SPADs (needed for automotive autonomous navigation market, industrial control, consumer electronics);
- Readout circuit for detecting photons coincidence (required for background light immunity on above mentioned markets);
- Solid-state sources of entangled photons are of interest for many applications beyond the boundary of quantum-physics experiments.
SUPERTWIN Hong-Ou-Mandel auto-correlator developed to test the solid-state sources.
SUPERTWIN super-twinning photon microscope building blocks and concept.
Entangled-photon detection with CMOS-SPAD array at University of Bern.