Error-mitigated variational algorithm on a photonic processor.

Our study demonstrates successful error mitigation of indistinguishably-related noise in a quantum photonic processor through the application of the zero-noise extrapolation (ZNE) technique. By measuring observable values at different error levels, we were able to extrapolate toward a noise-free regime. We examined the impact of partial distinguishability of photons in a two-qubit processor implementing the variational quantum eigensolver for a Schwinger Hamiltonian.

Robust Architecture for Programmable Universal Unitaries.

The decomposition of large unitary matrices into smaller ones is important because it provides ways to the realization of classical and quantum information processing schemes. Today, most of the methods use planar meshes of tunable two-channel blocks; however, the schemes turn out to be sensitive to fabrication errors. We study a novel decomposition method based on multichannel blocks.

Laser-written polarizing directional coupler with reduced interaction length.

Integrated optical waveguides, manufactured with femtosecond laser writing (FSLW) technology, enable precise control and manipulation of light in complicated photonic chips. However, due to the intrinsically low anisotropy of FSLW waveguides, polarizing integrated devices have had a relatively large footprint. In this Letter, we demonstrate an approach based on stress-induced anisotropy, allowing us to decrease the size of polarizing directional couplers down to 3.

Spatial Bell-State Generation without Transverse Mode Subspace Postselection.

Spatial states of single photons and spatially entangled photon pairs are becoming an important resource in quantum communication. This additional degree of freedom provides an almost unlimited information capacity, making the development of high-quality sources of spatial entanglement a well-motivated research direction. We report an experimental method for generation of photon pairs in a maximally entangled spatial state.

Anisotropically and high entanglement of biphoton states generated in spontaneous parametric down-conversion.

We show both theoretically and experimentally that biphoton wave packets generated via spontaneous parametric down-conversion can be strongly anisotropic and highly entangled. The conditions under which these effects exist are found and discussed.

Realization of four-level qudits using biphotons.

The novel experimental realization of four-level optical quantum systems (ququarts) is presented. We exploit the polarization properties of the frequency nondegenerate biphoton field to obtain such systems. A simple method that does not rely on am interferometer is used to generate and measure the sequence of states that can be used in quantum key distribution protocol.