48 research outputs found
Experimental multiphase estimation on a chip
Multiparameter estimation is a general problem that aims at measuring unknown
physical quantities, obtaining high precision in the process. In this context,
the adoption of quantum resources promises a substantial boost in the
achievable performances with respect to the classical case. However, several
open problems remain to be addressed in the multiparameter scenario. A crucial
requirement is the identification of suitable platforms to develop and
experimentally test novel efficient methodologies that can be employed in this
general framework. We report the experimental implementation of a
reconfigurable integrated multimode interferometer designed for the
simultaneous estimation of two optical phases. We verify the high-fidelity
operation of the implemented device, and demonstrate quantum-enhanced
performances in two-phase estimation with respect to the best classical case,
post-selected to the number of detected coincidences. This device can be
employed to test general adaptive multiphase protocols due to its high
reconfigurability level, and represents a powerful platform to investigate the
multiparameter estimation scenario.Comment: 10+7 pages, 7+4 figure
Integrated sources of entangled photons at telecom wavelength in femtosecond-laser-written circuits
Photon entanglement is an important state of light that is at the basis of
many protocols in photonic quantum technologies, from quantum computing, to
simulation and sensing. The capability to generate entangled photons in
integrated waveguide sources is particularly advantageous due to the enhanced
stability and more efficient light-crystal interaction. Here we realize an
integrated optical source of entangled degenerate photons at telecom
wavelength, based on the hybrid interfacing of photonic circuits in different
materials, all inscribed by femtosecond laser pulses. We show that our source,
based on spontaneous parametric down-conversion, gives access to different
classes of output states, allowing to switch from path-entangled to
polarization-entangled states with net visibilities above 0.92 for all selected
combinations of integrated devices
Adaptive phase estimation through a genetic algorithm
Quantum metrology is one of the most relevant applications of quantum information theory to quantum technologies. Here, quantum probes are exploited to overcome classical bounds in the estimation of unknown parameters. In this context, phase estimation, where the unknown parameter is a phase shift between two modes of a quantum system, is a fundamental problem. In practical and realistic applications, it is necessary to devise methods to optimally estimate an unknown phase shift by using a limited number of probes. Here we introduce and experimentally demonstrate a machine learning-based approach for the adaptive estimation of a phase shift in a Mach-Zehnder interferometer, tailored for optimal performances with limited resources. The employed technique is a genetic algorithm used to devise the optimal feedback phases employed during the estimation in an offline fashion. The results show the capability to retrieve the true value of the phase by using few photons, and to reach the sensitivity bounds in such small probe regime. We finally investigate the robustness of the protocol with respect to common experimental errors, showing that the protocol can be adapted to a noisy scenario. Such approach promises to be a useful tool for more complex and general tasks where optimization of feedback parameters is required
Photonic Quantum Metrology
Quantum Metrology is one of the most promising application of quantum
technologies. The aim of this research field is the estimation of unknown
parameters exploiting quantum resources, whose application can lead to enhanced
performances with respect to classical strategies. Several physical quantum
systems can be employed to develop quantum sensors, and photonic systems
represent ideal probes for a large number of metrological tasks. Here we review
the basic concepts behind quantum metrology and then focus on the application
of photonic technology for this task, with particular attention to phase
estimation. We describe the current state of the art in the field in terms of
platforms and quantum resources. Furthermore, we present the research area of
multiparameter quantum metrology, where multiple parameters have to be
estimated at the same time. We conclude by discussing the current experimental
and theoretical challenges, and the open questions towards implementation of
photonic quantum sensors with quantum-enhanced performances in the presence of
noise.Comment: 51 pages, 9 figures, 967 references. Comments and feedbacks are very
welcom
Machine-learning-based device-independent certification of quantum networks
Witnessing nonclassical behavior is a crucial ingredient in quantum information processing. For that, one has to optimize the quantum features a given physical setup can give rise to, which is a hard computational task currently tackled with semidefinite programming, a method limited to linear objective functions and that becomes prohibitive as the complexity of the system grows. Here, we propose an alternative strategy, which exploits a feedforward artificial neural network to optimize the correlations compatible with arbitrary quantum networks. A remarkable step forward with respect to existing methods is that it deals with nonlinear optimization constraints and objective functions, being applicable to scenarios featuring independent sources and nonlinear entanglement witnesses. Furthermore, it offers a significant speedup in comparison with other approaches, thus allowing to explore previously inaccessible regimes. We also extend the use of the neural network to the experimental realm, a situation in which the statistics are unavoidably affected by imperfections, retrieving device-independent uncertainty estimates on Bell-like violations obtained with independent sources of entangled photon states. In this way, this work paves the way for the certification of quantum resources in networks of growing size and complexity
Non-asymptotic Heisenberg scaling: experimental metrology for a wide resources range
Adopting quantum resources for parameter estimation discloses the possibility
to realize quantum sensors operating at a sensitivity beyond the standard
quantum limit. Such approach promises to reach the fundamental Heisenberg
scaling as a function of the employed resources in the estimation process.
Although previous experiments demonstrated precision scaling approaching
Heisenberg-limited performances, reaching such regime for a wide range of
remains hard to accomplish. Here, we show a method which suitably allocates the
available resources reaching Heisenberg scaling without any prior information
on the parameter. We demonstrate experimentally such an advantage in measuring
a rotation angle. We quantitatively verify Heisenberg scaling for a
considerable range of by using single-photon states with high-order orbital
angular momentum, achieving an error reduction greater than dB below the
standard quantum limit. Such results can be applied to different scenarios,
opening the way to the optimization of resources in quantum sensing
Optimizing quantum-enhanced Bayesian multiparameter estimation in noisy apparata
Achieving quantum-enhanced performances when measuring unknown quantities
requires developing suitable methodologies for practical scenarios, that
include noise and the availability of a limited amount of resources. Here, we
report on the optimization of quantum-enhanced Bayesian multiparameter
estimation in a scenario where a subset of the parameters describes unavoidable
noise processes in an experimental photonic sensor. We explore how the
optimization of the estimation changes depending on which parameters are either
of interest or are treated as nuisance ones. Our results show that optimizing
the multiparameter approach in noisy apparata represents a significant tool to
fully exploit the potential of practical sensors operating beyond the standard
quantum limit for broad resources range
Air-core fiber distribution of hybrid vector vortex-polarization entangled states
Entanglement distribution between distant parties is one of the most
important and challenging tasks in quantum communication. Distribution of
photonic entangled states using optical fiber links is a fundamental building
block towards quantum networks. Among the different degrees of freedom, orbital
angular momentum (OAM) is one of the most promising due to its natural
capability to encode high dimensional quantum states. In this article, we
experimentally demonstrate fiber distribution of hybrid polarization-vector
vortex entangled photon pairs. To this end, we exploit a recently developed
air-core fiber which supports OAM modes. High fidelity distribution of the
entangled states is demonstrated by performing quantum state tomography in the
polarization-OAM Hilbert space after fiber propagation, and by violations of
Bell inequalities and multipartite entanglement tests. The present results open
new scenarios for quantum applications where correlated complex states can be
transmitted by exploiting the vectorial nature of light
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