Orbital angular momentum based intra- and interparticle entangled states generated via a quantum dot source

Engineering single-photon states endowed with orbital angular momentum (OAM) is a powerful toolfor quantum information photonic implementations. Indeed, due to its unbounded nature, OAM is suitable forencoding qudits, allowing a single carrier to transport a large amount of information. Most of the experimentalplatforms employ spontaneous parametric down-conversion processes to generate single photons, evenif this approach is intrinsically probabilistic, leading to scalability issues for an increasing number of qudits.Semiconductor quantum dots (QDs) have been used to get over these limitations by producing on-demand pure and indistinguishable single-photon states, although only recently they have been exploitedto create OAM modes. Our work employs a bright QD single-photon source to generate a complete set ofquantum states for information processing with OAM-endowed photons. We first study hybrid intraparticleentanglement between OAM and polarization degrees of freedom of a single photon whose preparationwas certified by means of Hong–Ou–Mandel visibility. Then, we investigate hybrid interparticle OAM-based entanglement by exploiting a probabilistic entangling gate. The performance of our approach isassessed by performing quantum state tomography and violating Bell inequalities. Our results pave theway for the use of deterministic sources for the on-demand generation of photonic high-dimensionalquantum states.

Thermally reconfigurable quantum photonic circuits at telecom wavelength by femtosecond laser micromachining

The importance of integrated quantum photonics in the telecom band is based on the possibility of interfacing with the optical network infrastructure that was developed for classical communications.In this framework,femtosecond laser-written integrated photonic circuits,which have already been assessed for use in quantum information experiments in the 800-nm wavelength range,have great potential.In fact,these circuits,being written in glass,can be perfectly mode-matched at telecom wavelength to the in/out coupling fibers,which is a key requirement for a low-loss processing node in future quantum optical networks.In addition,for several applications,quantum photonic devices must be dynamically reconfigurable.Here,we experimentally demonstrate the high performance of femtosecond laser-written photonic circuits for use in quantum experiments in the telecom band,and we demonstrate the use of thermal shifters,which were also fabricated using the same femtosecond laser,to accurately tune such circuits.State-of-the-art manipulation of single-and two-photon states is demonstrated,with fringe visibilities greater than 95%.The results of this work open the way to the realization of reconfigurable quantum photonic circuits based on this technological platform.

Dynamical learning of a photonics quantum-state engineering process

Experimental engineering of high-dimensional quantum states is a crucial task for several quantum information protocols.However,a high degree of precision in the characterization of the noisy experimental apparatus is required to apply existing quantum-state engineering protocols.This is often lacking in practical scenarios,affecting the quality of the engineered states.We implement,experimentally,an automated adaptive optimization protocol to engineer photonic orbital angular momentum(OAM)states.The protocol,given a target output state,performs an online estimation of the quality of the currently produced states,relying on output measurement statistics,and determines how to tune the experimental parameters to optimize the state generation.To achieve this,the algorithm does not need to be imbued with a description of the generation apparatus itself.Rather,it operates in a fully black-box scenario,making the scheme applicable in a wide variety of circumstances.The handles controlled by the algorithm are the rotation angles of a series of waveplates and can be used to probabilistically generate arbitrary four-dimensional OAM states.We showcase our scheme on different target states both in classical and quantum regimes and prove its robustness to external perturbations on the control parameters.This approach represents a powerful tool for automated optimizations of noisy experimental tasks for quantum information protocols and technologies.