33 research outputs found
Characterization of multimode linear optical networks
Multimode optical interferometers represent the most viable platforms for the successful implementation of several quantum information schemes that take advantage of optical processing. Examples range from quantum communication and sensing, to computation, including optical neural networks, optical reservoir computing, or simulation of complex physical systems. The realization of such routines requires high levels of control and tunability of the parameters that define the operations carried out by the device. This requirement becomes particularly crucial in light of recent technological improvements in integrated photonic technologies, which enable the implementation of progressively larger circuits embedding a considerable amount of tunable parameters. We formulate efficient procedures for the characterization of optical circuits in the presence of imperfections that typically occur in physical experiments, such as unbalanced losses and phase instabilities in the input and output collection stages. The algorithm aims at reconstructing the transfer matrix that represents the optical interferometer without making any strong assumptions about its internal structure and encoding. We show the viability of this approach in an experimentally relevant scenario, defined by a tunable integrated photonic circuit, and we demonstrate the effectiveness and robustness of our method. Our findings can find application in a wide range of optical setups, based on both bulk and integrated configurations
Quantum state engineering using one-dimensional discrete-time quantum walks
Quantum state preparation in high-dimensional systems is an essential
requirement for many quantum-technology applications. The engineering of an
arbitrary quantum state is, however, typically strongly dependent on the
experimental platform chosen for implementation, and a general framework is
still missing. Here we show that coined quantum walks on a line, which
represent a framework general enough to encompass a variety of different
platforms, can be used for quantum state engineering of arbitrary
superpositions of the walker's sites. We achieve this goal by identifying a set
of conditions that fully characterize the reachable states in the space
comprising walker and coin, and providing a method to efficiently compute the
corresponding set of coin parameters. We assess the feasibility of our proposal
by identifying a linear optics experiment based on photonic orbital angular
momentum technology.Comment: 9 + 2 pages, 9 figure
Certification of Gaussian Boson Sampling via graphs feature vectors and kernels
Gaussian Boson Sampling (GBS) is a non-universal model for quantum computing inspired by the original formulation of the Boson Sampling (BS) problem. Nowadays, it represents a paradigmatic quantum platform to reach the quantum advantage regime in a specific computational model. Indeed, thanks to the implementation in photonics-based processors, the latest GBS experiments have reached a level of complexity where the quantum apparatus has solved the task faster than currently up-to-date classical strategies. In addition, recent studies have identified possible applications beyond the inherent sampling task. In particular, a direct connection between photon counting of a genuine GBS device and the number of perfect matchings in a graph has been established. In this work, we propose to exploit such a connection to benchmark GBS experiments. We interpret the properties of the feature vectors of the graph encoded in the device as a signature of correct sampling from the true input state. Within this framework, two approaches are presented. The first method exploits the distributions of graph feature vectors and classification via neural networks. The second approach investigates the distributions of graph kernels. Our results provide a novel approach to the actual need for tailored algorithms to benchmark large-scale Gaussian Boson Samplers
Quantum teleportation of a genuine vacuum-one-photon qubit generated via a quantum dot source
Quantum state teleportation represents a pillar of quantum information and a
milestone on the roadmap towards quantum networks with a large number of nodes.
Successful photonic demonstrations of this protocol have been carried out
employing different qubit encodings. However, demonstrations in the Fock basis
encoding are challenging, due to the impossibility of creating a coherent
superposition of vacuum-one photon states on a single mode with linear optics.
Previous realizations using such an encoding strongly relied on ancillary modes
of the electromagnetic field, which only allowed the teleportation of
subsystems of entangled states. Here, we enable quantum teleportation of
genuine vacuum-one photon states avoiding ancillary modes, by exploiting
coherent control of a resonantly excited semiconductor quantum dot in a
micro-cavity. Within our setup, we can teleport vacuum-one-photon qubits and
perform entanglement swapping in such an encoding. Our results may disclose new
potentialities of quantum dot single-photon sources for quantum information
applications.Comment: 10 pages, 4 figures + Supplementary Informatio
Dynamical learning of a photonics quantum-state engineering process
Abstract. 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.
Keywords: orbital angular momentum; state engineering; black-box optimization; algorithm; quantum
Witnesses of coherence and dimension from multiphoton indistinguishability tests
Quantum coherence marks a deviation from classical physics, and has been studied as a resource for metrology and quantum computation. Finding reliable and effective methods for assessing its presence is then highly desirable. Coherence witnesses rely on measuring observables whose outcomes can guarantee that a state is not diagonal in a known reference basis. Here, we experimentally measure a type of coherence witness that uses pairwise state comparisons to identify superpositions in a basis-independent way. Our experiment uses a single interferometric setup to simultaneously measure the three pairwise overlaps among three single-photon states via Hong-Ou-Mandel tests. Aside from coherence witnesses, we show the measurements also serve as a Hilbert-space dimension witness. Our results attest to the effectiveness of pooling many two-state comparison tests to ascertain various relational properties of a set of quantum states
Experimental quantification of genuine four-photon indistinguishability
Photon indistinguishability plays a fundamental role in information
processing, with applications such as linear-optical quantum computation and
metrology. It is then necessary to develop appropriate tools to quantify the
amount of this resource in a multiparticle scenario. Here we report a
four-photon experiment in a linear-optical interferometer designed to
simultaneously estimate the degree of indistinguishability between three pairs
of photons. The interferometer design dispenses with the need of heralding for
parametric down-conversion sources, resulting in an efficient and reliable
optical scheme. We then use a recently proposed theoretical framework to
quantify genuine four-photon indistinguishability, as well as to obtain bounds
on three unmeasured two-photon overlaps. Our findings are in high agreement
with the theory, and represent a new resource-effective technique for the
characterization of multiphoton interference.Comment: 8+8 pages, 5+5 figure