44 research outputs found
Multi-Photon Entanglement
Major efforts in quantum information science are devoted to the development of methods that are superior to the one of classical information processing, for example the quantum computer or quantum simulations. For these purposes, superposition and entangled states are considered a decisive resource. Furthermore, since the early days of quantum mechanics, entanglement has revealed the discrepancy between the quantum mechanical and the everyday life perception of the physical world. This combination of fundamental science and application-oriented research makes the realization, characterization, and application of entanglement a challenge pursued by many researchers.
In this work, the observation of entangled states of polarization encoded photonic qubits is pushed forward in two directions: flexibility in state observation and increase in photon rate. To achieve flexibility two different schemes are developed: setup-based and entanglement-based observation of inequivalent multi-photon states. The setup-based scheme relies on multi-photon interference at a polarizing beam splitter with prior polarization manipulations. It allows the observation of a family of important four-photon entangled states. The entanglement-based scheme exploits the rich properties of Dicke states under particle projections or loss in order to obtain inequivalent multi-photon entangled states. The observed states are characterized using the fidelity and entanglement witnesses.
An increase in photon rate is crucial to achieve entanglement of higher photon numbers. This holds especially, when photon sources are utilized that emit photons spontaneously. To this end, a new photon source is presented based on a femtosecond ultraviolet enhancement cavity and applied to the observation of the six-photon Dicke state with three excitations.
The implemented schemes not only allow the observation of inequivalent types of entanglement, but also the realization of various quantum information tasks. In this work, the four-photon GHZ state has been used in a quantum simulation of a minimal instance of the toric code. This code enables the demonstration of basic properties of anyons, which are quasiparticles distinct from bosons and fermions. Further, the six-photon Dicke state has been applied for quantum metrology: It allows one to estimate a phase shift with a higher precision than by using only classical resources.
Altogether, a whole series of experiments for observing inequivalent multi-photon entangled states can now be substituted by a single experimental setup based on the designs developed in this work. In addition to this new approach of photon processing, a novel photon source has been implemented, paving the way to realizations of applications requiring higher photon numbers.This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the Ludwig-Maximilians-Universität München's products or services. Internal or personal use of this material is permitted. However, permission to reprint republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this material, you agree to all provisions of the copyright laws protecting it
Vibrational signatures for the identification of single-photon emitters in hexagonal boron nitride
Color centers in h-BN are among the brightest emission centers known yet the
origins of these emission centers are not well understood. Here, using
first-principles calculations in combination with the generating function
method, we systematically elucidate the coupling of specific defects to the
vibrational degrees of freedom. We show that the lineshape of many defects
exhibits strong coupling to high frequency phonon modes and that
C, C, C-C dimer and
V can be associated with experimental lineshapes. Our detailed
theoretical study serves as a guide to identify optically active defects in
h-BN that can suit specific applications in photonic-based quantum
technologies, such as single photon emitters, hybrid spin-photon interfaces, or
spin-mechanics interfaces.Comment: 14 pages, 9 figure
Multi-qubit entanglement engineering via projective measurements
So far, various multi-photon entangled states have been observed
experimentally by using different experimental set-ups. Here, we present a
scheme to realize many SLOCC-inequivalent states of three and four qubits via
projective measurements on suitable entangled states. We demonstrate how these
states can be observed experimentally in a single set-up and study the
feasibility of the implementation with present-day technology
Cavity optomechanics with photonic bound states in the continuum
We propose a versatile, free-space cavity optomechanics platform built from two photonic crystal membranes, one of which is freely suspended, and designed to form a microcavity less than one wavelength long. This cavity features a series of photonic bound states in the continuum that, in principle, trap light forever and can be favorably used together with evanescent coupling for realizing various types of optomechanical couplings, such as linear or quadratic coupling of either dispersive or dissipative type, by tuning the photonic crystal patterning and cavity length. Crucially, this platform allows for a quantum cooperativity exceeding unity in the ultrastrong single-photon coupling regime, surpassing the performance of conventional Fabry-Perot-based cavity optomechanical devices in the nonresolved sideband regime. This platform allows for exploring new regimes of the optomechanical interaction, in particular in the framework of pulsed and single-photon optomechanics
Pulsed Laser Cooling for Cavity-Optomechanical Resonators
A pulsed cooling scheme for optomechanical systems is presented that is
capable of cooling at much faster rates, shorter overall cooling times, and for
a wider set of experimental scenarios than is possible by conventional methods.
The proposed scheme can be implemented for both strongly and weakly coupled
optomechanical systems in both weakly and highly dissipative cavities. We study
analytically its underlying working mechanism, which is based on
interferometric control of optomechanical interactions, and we demonstrate its
efficiency with pulse sequences that are obtained by using methods from optimal
control. The short time in which our scheme approaches the optomechanical
ground state allows for a significant relaxation of current experimental
constraints. Finally, the framework presented here can be used to create a rich
variety of optomechanical interactions and hence offers a novel, readily
available toolbox for fast optomechanical quantum control.Comment: 6 pages, 4 figure
Discriminating multi-partite entangled states
The variety of multi-partite entangled states enables numerous applications
in novel quantum information tasks. In order to compare the suitability of
different states from a theoretical point of view classifications have been
introduced. Accordingly, here we derive criteria and demonstrate how to
experimentally discriminate an observed state against the ones of certain other
classes of multi-partite entangled states. Our method, originating in Bell
inequalities, adds an important tool for the characterization of multi-party
entanglement.Comment: 4 pages, 1 figur
Practical methods for witnessing genuine multi-qubit entanglement in the vicinity of symmetric states
We present general numerical methods to construct witness operators for
entanglement detection and estimation of the fidelity. Our methods are applied
to detecting entanglement in the vicinity of a six-qubit Dicke state with three
excitations and also to further entangled symmetric states. All our witnesses
are designed to keep the measurement effort small. We present also general
results on the efficient local decomposition of permutationally invariant
operators, which makes it possible to measure projectors to symmetric states
efficientlyComment: 13 pages including 4 figures, revtex
Optimal state estimation for cavity optomechanical systems
We demonstrate optimal state estimation for a cavity optomechanical system
through Kalman filtering. By taking into account nontrivial experimental noise
sources, such as colored laser noise and spurious mechanical modes, we
implement a realistic state-space model. This allows us to obtain the
conditional system state, i.e., conditioned on previous measurements, with
minimal least-square estimation error. We apply this method for estimating the
mechanical state, as well as optomechanical correlations both in the weak and
strong coupling regime. The application of the Kalman filter is an important
next step for achieving real-time optimal (classical and quantum) control of
cavity optomechanical systems.Comment: replaced with published version, 5+12 page
Experimental implementation of a four-player quantum game
Game theory is central to the understanding of competitive interactions
arising in many fields, from the social and physical sciences to economics.
Recently, as the definition of information is generalized to include entangled
quantum systems, quantum game theory has emerged as a framework for
understanding the competitive flow of quantum information. Up till now only
two-player quantum games have been demonstrated. Here we report the first
experiment that implements a four-player quantum Minority game over tunable
four-partite entangled states encoded in the polarization of single photons.
Experimental application of appropriate quantum player strategies give
equilibrium payoff values well above those achievable in the classical game.
These results are in excellent quantitative agreement with our theoretical
analysis of the symmetric Pareto optimal strategies. Our result demonstrate for
the first time how non-trivial equilibria can arise in a competitive situation
involving quantum agents and pave the way for a range of quantum transaction
applications.Comment: 9 pages, 5 figure