Since the first quantum ghost imaging (QGI) experiment in 1995, many QGI schemes have been put forward. However, the position-position or momentum-momentum correlation required in these QGI schemes cannot be distributed over optical fibers, which limits their large-scale geographical applications. In this paper, we propose and demonstrate a scheme for long-distance QGI utilizing frequency correlated photon pairs. In this scheme, the frequency correlation is transformed to the correlation between the illuminating position of one photon and the arrival time of the other photon, by which QGI can be realized in the time domain. Since frequency correlation can be preserved when the photon pairs are distributed over optical fibers, this scheme provides a way to realize long-distance QGI over large geographical scale. In the experiment, long-distance QGI over 50 km optical fibers has been demonstrated.
Since the first quantum ghost imaging (QGI) experiment in 1995, many QGI schemes have been put forward. However, the position-position or momentum-momentum correlation required in these QGI schemes cannot be distributed over optical fibers, which limits their large-scale geographical applications. In this paper, we propose and demonstrate a scheme for long-distance QGI utilizing frequency correlated photon pairs. In this scheme, the frequency correlation is transformed to the correlation between the illuminating position of one photon and the arrival time of the other photon, by which QGI can be realized in the time domain. Since frequency correlation can be preserved when the photon pairs are distributed over optical fibers, this scheme provides a way to realize long-distance QGI over large geographical scale. In the experiment, long-distance QGI over 50 km optical fibers has been demonstrated.
A thermal ghost imaging scheme between two distant parties is proposed and experimentally demonstrated over long-distance optical fibers. In the scheme, the weak thermal light is split into two paths. Photons in one path are spatially diffused according to their frequencies by a spatial dispersion component, then illuminate the object and record its spatial transmission information. Photons in the other path are temporally diffused by a temporal dispersion component. By the coincidence measurement between photons of two paths, the object can be imaged in a way of ghost imaging, based on the frequency correlation between photons in the two paths. In the experiment, the weak thermal light source is prepared by the spontaneous four-wave mixing in a silicon waveguide. The temporal dispersion is introduced by single-mode fibers of 50 km, which also could be looked at as a fiber link. Experimental results show that this scheme can be realized over long-distance optical fibers.
Quantum Ghost Imaging (QGI) is a scheme using entangled pairs of photons (signal and idler) in order to perform imaging with both single photons and with only a single-element detector in the spectrum of interest. It utilises the temporal coincidence of the photons to identify associated pairs, while their spatial correlation allows to obtain image information from of the idler photon from the measurement of the signal photon. It is especially useful when using nondegenerate photon pairs, allowing to keep the signal photon in the silicon detection window, while the interacting wavelength can be freely chosen.However, current schemes are limited, as they rely on time-gating and heralding. Recent advances in single photon avalanche diodes (SPADs) allow the design of new single photon cameras, which can be outfitted with dedicated in-pixel timing circuitry. This allows to register single photons in both time and space. These detectors allowed us to design a new scheme for QGI, in which the coincidence is evaluated after the measurement. It also allows us to perform depth-resolved 3D imaging based on the time-of-flight of photons, first results of which are presented here.
Quantum Ghost Imaging (QGI) is a scheme which uses the temporal correlation of entangled photon pairs (signal and idler) to identify detections belonging to actual entangled pairs and separate them from uncorrelated detections. By also exploiting the spatial correlation of the photon pair, this identification allows to extract image information of the idler photons by imaging the signal photons. This can even be done for non-degenerate photon pairs, allowing imaging at wavelengths without sophisticated cameras in this regime. Recent advances in detector technology, especially single photon avalanche diodes (SPADs), allow the design for new cameras capable of single photon detection with both high spatial and temporal resolution. These new detectors are especially useful for application in QGI, allowing to detect each photon individually and identify the correlated pairs after the measurement. It further allows to analyse the time-of-flight of photons and thus enables 3D imaging, the first realization of which will be presented here.
Low-light-level imaging in the infrared regime could find applications in areas ranging from technological to biological. Still, its development is limited by the inefficiency of silicon-based detectors in this regime. Quantum Ghost Imaging (QGI) can address this limitation by allowing the separation of illumination and imaging [1]. This is accomplished by generating non-degenerate correlated photon pairs, whose infrared photon probes the object and is detected by an InGaAs bucket detector, while the spatial distribution of the visible one is collected by a single-photon sensitive silicon camera. Traditional QGI setups evaluate photon correlations through “heralding”, by triggering the camera upon idler detection and thus require an image-preserving delay-line, which limits their use for remote sensing [1]. In asynchronous QGI (aQGI) cameras are replaced with SPAD arrays [2] able to record photon timestamp with picoseconds precision. By identifying pairs through timestamps comparison, the mentioned limitations are resolved [3], enabling applications with reflective or diffusive objects where the timestamp delay depends on the object's position. In this work, we propose and demonstrate an experimental QGI setup for remote sensing in reflection configuration (Fig. 1). Collinear non-degenerate pairs of single-photons at 550 nm and 1550 nm are generated by pumping a 2 mm-long type-0 ppKTP crystal with a 405 nm laser. To enable imaging of objects at varying distances, we implemented a momentum-correlation-based setup. Infrared photons interacting with the object were collected by commercially available InGaAs SPAD detectors, while the visible photons were directly captured using a prototype silicon SPAD array developed by Politecnico di Milano [4]. It is based on a 32×32 SPAD, with in-pixel TDCs, and on-chip microlenses are employed to reach a fill factor of 78%. The time resolution is adjustable down to 250 ps, with 1 μs Full Scale Range (FSR). The measurement duty cycle (i.e. the ration of the TDC FSR and the frame time) can be increased with a multi-gate acquisition scheme. To validate the efficiency of our setup, we tested it using a proof-of-principle object, as shown in Fig. 1b. The reconstructed images, captured with the object placed at 30 cm intervals in an acquisition time of only 30 s, are shown in Fig. 1c. In summary, the shown results confirm the potential of the proposed setup for remote sensing applications, particularly for reflective or diffusive objects. Moreover, the proposed approach could offers the possibility of significantly reduce acquisition times compared to standard QGI setups.
Quantum ghost imaging (QGI) leverages correlations between entangled photon pairs to reconstruct an image using light that has never physically interacted with an object. Despite extensive research interest, this technique has long been hindered by slow acquisition speeds, due to the use of raster-scanned detectors or the slow response of intensified cameras. Here, we utilize a single-photon-sensitive time-stamping camera to perform QGI at ultra-low-light levels with rapid data acquisition and processing times, achieving high-resolution and high-contrast images in under 1 min. Our work addresses the trade-off between image quality, optical power, data acquisition time, and data processing time in QGI, paving the way for practical applications in biomedical and quantum-secured imaging.
This talk introduces our recent works on how to use photonic energy-time entanglement in quantum communications. On one hand, we realized entanglement based dispersive optics quantum key distribution over optical fibers of 20 kilometers, in which time encoding based on energy-time entanglement was used. On the other hand, we proposed and demonstrated a scheme of temporal quantum ghost imaging, which could be realized by correlations in either frequency or time in energy-time entangled photon pairs. Based on it, a scheme of quantum secure ghost imaging was proposed and demonstrated, and it was applied on a new protocol of multi-bit QDS recently.