Michał Jachura

Bandwidth manipulation of quantum light by an electro-optic time lens

By employing electro-optic phase modulation, a time-lens imaging system is demonstrated for single-photon pulses. Such a system achieves wavelength-preserving sixfold bandwidth compression of single-photon states in the near-infrared spectral region.

Shot-by-shot imaging of Hong-Ou-Mandel interference with an intensified sCMOS camera.

We report the first observation of Hong-Ou-Mandel (HOM) interference of highly indistinguishable photon pairs with spatial resolution. Direct imaging of two-photon coalescence with an intensified sCMOS camera system clearly reveals spatially separated photons appearing pairwise within one of the two modes. With the use of the camera system, we quantified the number of pairs and recovered the full HOM dip yielding 96.3% interference visibility, as well as counted the number of coalesced pairs. We retrieved the spatial modes of both interfering photons by performing a proof-of-principle demonstration of a new, low-noise, high-resolution coincidence imaging scheme.

Hologram of a single photon

The local amplitude and phase of a single photon is retrieved using a method similar to classical holography. The interference of optical fields is replaced by the non-classical interference of spatially varying two-photon probability amplitudes.

Mode engineering for realistic quantum-enhanced interferometry

Quantum metrology overcomes standard precision limits by exploiting collective quantum superpositions of physical systems used for sensing, with the prominent example of non-classical multiphoton states improving interferometric techniques. Practical quantum-enhanced interferometry is, however, vulnerable to imperfections such as partial distinguishability of interfering photons. Here we introduce a method where appropriate design of the modal structure of input photons can alleviate deleterious effects caused by another, experimentally inaccessible degree of freedom. This result is accompanied by a laboratory demonstration that a suitable choice of spatial modes combined with position-resolved coincidence detection restores entanglement-enhanced precision in the full operating range of a realistic two-photon Mach–Zehnder interferometer, specifically around a point which otherwise does not even attain the shot-noise limit due to the presence of residual distinguishing information in the spectral degree of freedom. Our method highlights the potential of engineering multimode physical systems in metrologic applications. Quantum interferometry suffers from residual distinguishability between input photons. Here, the authors show theoretically and experimentally, in a two-photon measurement, how to overcome this by manipulating additional degrees of freedom.

High-visibility nonclassical interference of photon pairs generated in a multimode nonlinear waveguide

We report measurements of two-photon interference using a cw-pumped type-II spontaneous parametric down-conversion source based on a multimode perodically poled potassium titanyl phosphate (PPKTP) waveguide. We have used the recently demonstrated technique of controlling the spatial characteristics of the down-conversion process via intermodal dispersion to generate photon pairs in fundamental transverse modes, thus ensuring their spatial indistinguishability. Good overlap of photon modes within the pairs has been verified using the Hong-Ou-Mandel interferometer and the preparation of polarization entanglement in the Shih-Alley configuration, yielding visibilities consistently above 90%.

Bright integrated photon-pair source for practical passive decoy-state quantum key distribution

We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order

Quantum fingerprinting using two-photon interference

n

Quantum memory receiver for superadditive communication using binary coherent states

-photon states up to

Generation and characterization of discrete spatial entanglement in multimode nonlinear waveguides

n=4

Optimizing deep-space optical communication under power constraints

. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks.