Generation Of Multi-photon States Research Articles

Real‐Time Superresolution Interferometric Measurement Enabled by Structured Nonlinear Optics

AbstractOptical interferometers are pillars of modern precision metrology, but their resolution is limited by the wavelength of the light source, which cannot be infinitely reduced. Magically, this limitation can be circumvented by using an entangled multiphoton source because interference produced by an N‐photon amplitude features a reduced de Broglie wavelength . However, the extremely low efficiency in multiphoton state generation and coincidence counts actually negates the potential of using multiphoton states in practical measurements. Here, a novel interferometric technique based on structured nonlinear optics is demonstrated, i.e., parametric upconversion of a structured beam, capable of superresolution measurement in real time. The main principle relies in that the orbital angular momentum (OAM) state and associated intramodal phase within the structured beam are both continuously multiplied in cascading upconversion to mimic the superresolved phase evolution of a multiphoton amplitude. Owing to the use of bright sensing beams and OAM mode projection, up to a 12‐photon de Broglie wavelength with almost perfect visibility is observed in real time and, importantly, by using only a low‐cost detector. The results open the door to real‐time superresolution interferometric metrology and provide a promising way toward multiphoton superiority in practical applications.

Research on broadband achromatic metalenses

<p indent=0mm>Nowadays, metasurfaces can be made into various classical and non-classical devices due to their plentiful physical connotation and application value. To optimize the design method of broadband continuous achromatism, we rely on the geometric phase and resonance phase of the metasurface to realize the separation of the wavelength-independent basic phase and the wavelength-dependent chromatic aberration phase in the optical device, and design the achromatic reflection focusing mirror and reflector in the near-infrared band. Next, we use the GaN nanopillars and its inverse structure which is transparent under visible light to prepare an achromatic metalens in the visible light frequency band, and for the first time achieve full-color imaging and video shooting based on metalenses. Faced with the problem that the numerical aperture and the clear aperture cannot be large at the same time, we bring in the system of metalens array, which not only obtains the improvement of the imaging effect, but also realizes the light field imaging, which greatly enriches the imaging of the metalens content and function. Recently, by integrating a metalens array with a nonlinear crystal, we demonstrate a 100-path spontaneous parametric down-conversion photon-pair source in a 10 × 10 array, which shows promise for high-dimensional entanglement and multiphoton-state generation. This quantum light source can realize both high-dimensional entanglement and multiphotons. The metalens has introduced new systems and new physical effects in the fields of optical imaging and quantum optics.

Interface between Trapped-Ion Qubits and Traveling Photons with Close-to-Optimal Efficiency

A near optimum system for entangled photon collection and absorption in a single trapped ion is experimentally achieved: High-efficiency is further demonstrated by the generation of multi-photon states with up to 15 photons.

Metalens-array-based high-dimensional and multiphoton quantum source.

The development of two-dimensional metasurfaces has shown great potential in quantum-optical technologies because of the excellent flexibility in light-field manipulation. By integrating a metalens array with a nonlinear crystal, we demonstrate a 100-path spontaneous parametric down-conversion photon-pair source in a 10 × 10 array, which shows promise for high-dimensional entanglement and multiphoton-state generation. We demonstrate two-, three- and four-dimensional two-photon path entanglement with different phases encoded by metalenses with fidelities of 98.4, 96.6, and 95.0%, respectively. Furthermore, four-photon and six-photon generation is observed with high indistinguishability of photons generated from different metalenses. Our metalens-array-based quantum photon source is compact, stable, and controllable, indicating a new platform for integrated quantum devices.

Tuning single-photon sources for telecom multi-photon experiments.

Multi-photon state generation is of great interest for near-future quantum simulation and quantum computation experiments. To-date spontaneous parametric down-conversion is still the most promising process, even though two major impediments still exist: accidental photon noise (caused by the probabilistic non-linear process) and imperfect single-photon purity (arising from spectral entanglement between the photon pairs). In this work, we overcome both of these difficulties by (1) exploiting a passive temporal multiplexing scheme and (2) carefully optimizing the spectral properties of the down-converted photons using periodically-poled KTP crystals. We construct two down-conversion sources in the telecom wavelength regime, finding spectral purities of > 91%, while maintaining high four-photon count rates. We use single-photon grating spectrometers together with superconducting nanowire single-photon detectors to perform a detailed characterization of our multi-photon source. Our methods provide practical solutions to produce high-quality multi-photon states, which are in demand for many quantum photonics applications.

Crossed-crystal scheme for femtosecond-pulsed entangled photon generation in periodically poled potassium titanyl phosphate

We demonstrate a novel scheme for femto-second pulsed spontaneous parametric down-conversion in periodically poled KTP crystals. Our scheme is based on a crossed crystal configuration with collinear quasi-phase-matching. The non-degenerate photon pairs are split in a fiber-based wavelength division multiplexer. The source is easier to align than common pulsed sources based on bulk BBO crystals and exhibits high-quality polarization entanglement as well as non-classical interference capabilities. Hence, we expect this source to be a well-suited candidate for multi-photon state generation e.g. for linear optical quantum computation and quantum communication networks.