Tom Wolterink

Programmable two-photon quantum interference in 10^3 channels in opaque scattering media

We investigate two-photon quantum interference in an opaque scattering medium that intrinsically supports a large number of transmission channels. By adaptive spatial phase modulation of the incident wave fronts, the photons are directed at targeted speckle spots or output channels. From 10 3 experimentally available coupled channels, we select two channels and enhance their transmission to realize the equivalent of a fully programmable 2×2 beam splitter. By sending pairs of single photons from a parametric down-conversion source through the opaque scattering medium, we observe two-photon quantum interference. The programed beam splitter need not fulfill energy conservation over the two selected output channels and hence could be nonunitary. Consequently, we have the freedom to tune the quantum interference from bunching (Hong-Ou-Mandel-like) to antibunching. Our results establish opaque scattering media as a platform for high-dimensional quantum interference that is notably relevant for boson sampling and physical-key-based authentication.

Programmable multiport optical circuits in opaque scattering materials

We propose and experimentally verify a method to program the effective transmission matrix of general multiport linear optical circuits in random multiple-scattering materials by phase modulation of incident wavefronts. We demonstrate the power of our method by programming linear optical circuits in white paint layers with 2 inputs and 2 outputs, and 2 inputs and 3 outputs. Using interferometric techniques we verify our ability to program any desired phase relation between the outputs. The method works in a deterministic manner and can be directly applied to existing wavefront-shaping setups without the need of measuring a transmission matrix or to rely on sensitive interference measurements.

Transmitting more than 10 bit with a single photon

Encoding information in the position of single photons has no known limits, given infinite resources. Using a heralded single-photon source and a spatial light modulator (SLM), we steer single photons to specific positions in a virtual grid on a large-area spatially resolving photon-counting detector (ICCD). We experimentally demonstrate selective addressing any location (symbol) in a 9072 size grid (alphabet) to achieve 10.5 bit of mutual information per detected photon between the sender and receiver. Our results can be useful for very-high-dimensional quantum information processing.

Quantum optics of lossy asymmetric beam splitters

We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2×2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers.

Controlling quantum correlations in massively multichannel optical networks

Quantum optics experiments require ultimate control over the propagation of light in linear optical networks to realize programmable photon correlations [1]. Integrated optics provides a robust and low-loss platform for implementing such linear optical networks. However, to achieve ultimate control on the quantum state of light, it is necessary to program the network [2]. Tuning the network for controlled multiphoton correlations involves optimization algorithms which scale inefficiently with the network size and photon number. Therefore, it is challenging to scale up this approach to massively multichannel networks, which are required for large-scale implementations of quantum information processing and quantum communication.

Secure communication with coded wavefronts

Communication between a sender and receiver can be made secure by encrypting the message using public or private shared keys. Quantum key distribution utilizes the unclonability of a quantum state to securely generate a key between the two parties [1]. However, without some way of authentication of either the sender or the receiver, a man-in-the-middle attack with an eavesdropper mimicking the receiver can break the security of the protocol.

Programmable quantum interference in complex optical networks realized in opaque scattering media

Light transport in opaque scattering media mixes the light across the large number of modes in the system. The mixing results in the scrambling of information encoded on the incident light, which is generally detrimental. However, the multimodal transport hints at the possibility of utilizing them as complex optical networks if the transport could be controlled. In recent years, wavefront shaping through adaptive phase control has been used to create multiport optical devices in opaque scattering media. We study the programmability of one such device created in opaque scattering medium, a two-port beam splitter which is a primitive for any complex linear optical network. Here, I will discuss our latest results on the quantum interference between single photons from an ultrabright quantum source at the two-port beam splitter. The novel feature of the realized beam splitter is the programmability of quantum interference between single photons, creating either bunched or anti-bunched light at the outputs. Our demonstration is a first step towards realizing complex optical networks with programmable quantum correlations using opaque scattering media.

Programming quantum interference with multiple scattering

Multiple-scattering has become an exciting platform for quantum optical experiments [1-5]. In wavefront shaping one uses spatial light modulation in combination with strongly scattering materials to achieve control over light in space and time [6]. Recent wavefront-shaping experiments have transformed opaque media in equivalents of waveguides, lenses, waveplates and optical pulse compressors that are inherently robust against disorder and imaging errors. In quantum optics, interference of quantum states is studied in often complicated optical circuits. This requires a close-to-perfect implementation of the setup and provides little flexibility or programmability of the interference. We implement the radically different approach to apply wavefront shaping on quantum light to obtain ample flexibility in optimization and manipulation of the quantum interference. This offers unique opportunities for sample characterization, quantum patterning, secure key generation, or quantum transport through disordered media.