19 research outputs found
Experimental signature of Quantum Darwinism in photonic cluster states
We report on an experimental assessment of the emergence of Quantum Darwinism
(QD) from engineered open-system dynamics. We use a photonic hyperentangled
source of graph states to address the effects that correlations among the
elements of a multi-party environment have on the establishment of objective
reality ensuing the quantum-to-classical transition. Besides embodying one of
the first experimental efforts towards the characterization of QD, our work
illustrates the non-trivial consequences that multipartite entanglement and, in
turn, the possibility of having environment-to-system back-action have on the
features of the QD framework.Comment: 5 pages, 5 figures, Revtex4-
Experimental generation of entanglement from classical correlations via non-unital local noise
We experimentally show how classical correlations can be turned into quantum
entanglement, via the presence of non-unital local noise and the action of a
CNOT gate. We first implement a simple two-qubit protocol in which entanglement
production is not possible in the absence of local non-unital noise, while
entanglement arises with the introduction of noise, and is proportional to the
degree of noisiness. We then perform a more elaborate four-qubit experiment, by
employing two hyperentangled photons initially carrying only classical
correlations. We demonstrate a scheme where the entanglement is generated via
local non-unital noise, with the advantage to be robust against local unitaries
performed by an adversary.Comment: 8 pages, 4 figure
Quantum-enhanced multiparameter estimation in multiarm interferometers
Quantum metrology is the state-of-the-art measurement technology. It uses
quantum resources to enhance the sensitivity of phase estimation beyond what
reachable within classical physics. While single parameter estimation theory
has been widely investigated, much less is known about the simultaneous
estimation of multiple phases, which finds key applications in imaging and
sensing. In this manuscript we provide conditions of useful entanglement (among
multimode particles, qudits) for multiphase estimation and adapt them to
multiarm Mach-Zehnder interferometry. We discuss benchmark multimode Fock
states containing useful qudit entanglement and overcoming the sensitivity of
separable qudit states in three and four arm Mach-Zehnder-like interferometers
- currently within the reach of integrated photonics technology.Comment: 7+3 pages, 4+2 figure
Path-polarization hyperentangled and cluster states of photons on a chip
Encoding many qubits in different degrees of freedom (DOFs) of single photons
is one of the routes towards enlarging the Hilbert space spanned by a photonic
quantum state. Hyperentangled photon states (i.e. states showing entanglement
in multiple DOFs) have demonstrated significant implications for both
fundamental physics tests and quantum communication and computation. Increasing
the number of qubits of photonic experiments requires miniaturization and
integration of the basic elements and functions to guarantee the set-up
stability. This motivates the development of technologies allowing the precise
control of different photonic DOFs on a chip. We demonstrate the contextual use
of path and polarization qubits propagating within an integrated quantum
circuit. We tested the properties of four-qubit linear cluster states built on
both DOFs. Our results pave the way towards the full integration on a chip of
hybrid multiqubit multiphoton states.Comment: 7 pages, 7 figures, RevTex4-1, Light: Science & Applications
AAP:http://aap.nature-lsa.cn:8080/cms/accessory/files/AAP-lsa201664.pd
Experimental nonlocality-based network diagnostics of mutipartite entangled states
Quantum networks of growing complexity play a key role as resources for
quantum computation; the ability to identify the quality of their internal
correlations will play a crucial role in addressing the buiding stage of such
states. We introduce a novel diagnostic scheme for multipartite networks of
entangled particles, aimed at assessing the quality of the gates used for the
engineering of their state. Using the information gathered from a set of
suitably chosen multiparticle Bell tests, we identify conditions bounding the
quality of the entangled bonds among the elements of a register. We demonstrate
the effectiveness, flexibility, and diagnostic power of the proposed
methodology by characterizing a quantum resource engineered combining
two-photon hyperentanglement and photonic-chip technology. Our approach is
feasible for medium-sized networks due to the intrinsically modular nature of
cluster states, and paves the way to section-by-section analysis of large
photonics resources.Comment: 5 pages, 3 figures, RevTex4-
Optimal measurements for simultaneous quantum estimation of multiple phases
A quantum theory of multiphase estimation is crucial for quantum-enhanced sensing and imaging and may link quantum metrology to more complex quantum computation and communication protocols. In this Letter, we tackle one of the key difficulties of multiphase estimation: obtaining a measurement which saturates the fundamental sensitivity bounds. We derive necessary and sufficient conditions for projective measurements acting on pure states to saturate the ultimate theoretical bound on precision given by the quantum Fisher information matrix. We apply our theory to the specific example of interferometric phase estimation using photon number measurements, a convenient choice in the laboratory. Our results thus introduce concepts and methods relevant to the future theoretical and experimental development of multiparameter estimation