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arXiv:1307.6826 · Journal of the Optical Society of America B

Preparation of km-photon concatenated Greenberger–Horne–Zeilinger states for observing distinctive quantum effects at macroscopic scales

Dong Ding, Fengli Yan, Ting Gao

Published Oct 30, 2013• 29 citations
arXivHTMLPDF

Abstract

Multipartite concatenated Greenberger–Horne–Zeilinger (C-GHZ) states, a class of multipartite entangled states, have superior stability under the influence of decoherence. We propose two means of constructing multiphoton C-GHZ states based on entanglers of multiphoton GHZ states that are both experimentally realizable and scalable. Given a km-photon GHZ state as an input state, if m is odd, one can create a km-photon C-GHZ state. In addition, we have designed a scheme to prepare km-photon C-GHZ states from km single-photon states by using k entanglers of m-photon GHZ states and km-control Toffoli gates.

DOI
10.1364/josab.30.003075

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Multipartite concatenated Greenberger–Horne–Zeilinger (C-GHZ) states, a class of multipartite entangled states, have superior stability under the influence of decoherence. We propose two means of constructing multiphoton C-GHZ states based on entanglers of multiphoton GHZ states that are both experimentally realizable and scalable. Given a km-photon GHZ state as an input state, if m is odd, one can create a km-photon C-GHZ state. In addition, we have designed a scheme to prepare km-photon C-GHZ states from km single-photon states by using k entanglers of m-photon GHZ states and km-control Toffoli gates.
We study the stability of superpositions of macroscopically distinct quantum states under decoherence. We introduce a class of quantum states with entanglement features similar to Greenberger-Horne-Zeilinger (GHZ) states, but with an inherent stability against noise and decoherence. We show that in contrast to GHZ states, these so-called concatenated GHZ states remain multipartite entangled even for macroscopic numbers of particles and can be used for quantum metrology in noisy environments. We also propose a scalable experimental realization of these states using existing ion-trap setups.
Abstract The concatenated Greenberger–Horne–Zeilinger (C-GHZ) state is a new kind of logic-qubit entangled state, which may have extensive applications in future quantum communication. In this letter, we propose a protocol for constructing an arbitrary C-GHZ state with single photons. We exploit the cross-Kerr nonlinearity for this purpose. This protocol has some advantages over previous protocols. First, it only requires two kinds of cross-Kerr nonlinearities to generate single phase shifts ± θ . Second, it is not necessary to use sophisticated m -photon Toffoli gates. Third, this protocol is deterministic and can be used to generate an arbitrary C-GHZ state. This protocol may be useful in future quantum information processing based on the C-GHZ state.
The multipartite Greenberger-Horne-Zeilinger (GHZ) state is a paradigmatic example of a highly entangled multipartite state with distinct quantum features. However, the GHZ state is very sensitive to generic decoherence processes, where its quantum features and, in particular, its entanglement diminish rapidly, thereby hindering possible practical applications. In this paper, we discuss GHZ-like quantum states with a block-local structure and show that they exhibit a drastically increased stability against noise for certain choices of block-encoding, thereby extending results of [Phys. Rev. Lett. 106, 110402 (2011)]. We analyze in detail the decay of the interference terms, the entanglement in terms of distillable entanglement, and negativity as well as the notion of macroscopicity as measured by the so-called index qqq and provide general bounds on these quantities. We focus on an encoding where logical qubits are themselves encoded as GHZ states, which leads to so-called concatenated GHZ (C-GHZ) states. We compare the stability of C-GHZ states with other types of encodings, thereby showing the superior stability of the C-GHZ states. Analytic results are complemented by numerical studies, where tensor network techniques are used to investigate the quantum properties of multipartite entangled states under the influence of decoherence.
One of the most important multipartite entangled states, Greenberger-Horne-Zeilinger state (GHZ), serves as a fundamental resource for quantum foundation test, quantum communication and quantum computation. To increase the number of entangled particles, significant experimental efforts should been invested due to the complexity of optical setup and the difficulty in maintaining the coherence condition for high-fidelity GHZ state. Here, we propose an ultra-integrated scalable on-chip GHZ state generation scheme based on frequency combs. By designing several microrings pumped by different lasers, multiple partially overlapped quantum frequency combs are generated to supply as the basis for on-chip polarization-encoded GHZ state with each qubit occupying a certain spectral mode. Both even and odd numbers of GHZ states can be engineered with constant small number of integrated components and easily scaled up on the same chip by only adjusting one of the pump wavelengths. In addition, we give the on-chip design of projection measurement for characterizing GHZ states and show the reconfigurability of the state. Our proposal is rather simple and feasible within the existing fabrication technologies and we believe it will boost the development of multiphoton technologies.
Greenberger-Horne-Zeilinger (GHZ) state is a typical maximally entangled state which is pursued in both fundamental research and emerging quantum technologies. Preparing large-scale GHZ states in lattice spin systems is particularly appealing for quantum advantages, but conventional schemes face great challenges in scalability. Here we propose a universal and scalable scheme to generate large-scale GHZ-like states, which share similar entanglement and metrological properties with standard GHZ states, in lattice spin systems through global Floquet engineering. Our scheme requires only global operations and shows great advantage for large particle number. It is applicable to systems with arbitrary interaction ranges, offering a practical pathway for large-scale implementation of many-body entangled states in various systems.
We present two schemes for realizing the remote preparation of a Greenberger–Horne–Zeilinger (GHZ) state. The first scheme is to remotely prepare a general N -particle GHZ state with two steps. One is to prepare a qubit state by using finite classical bits from sender to receiver via a two-particle entangled state, and the other is that the receiver introduces N — 1 additional particles and performs N — 1 controlled-not (C-Not) operations. The second scheme is to remotely prepare an N -atom GHZ state via a two-atom entangled state in cavity quantum electrodynamics (QED). The two schemes require only a two-particle entangled state used as a quantum channel, so we reduce the requirement for entanglement.