Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1012.4472 · Physical Review Letters

Stable Macroscopic Quantum Superpositions

Florian Fröwis, Wolfgang Dür

Published Mar 16, 2011• 100 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physrevlett.106.110402

Related papers

Stability of encoded macroscopic quantum superpositions

Florian Fröwis, Wolfgang Dür

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 $q$ 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.

arXiv:1201.2184•Physical Review A•May 29, 2012•31 citations

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

Dong Ding, Fengli Yan, Ting Gao

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.

arXiv:1307.6826•Journal of the Optical Society of America B•Oct 30, 2013•29 citations

Superposition of macroscopically distinct states means large multipartite entanglement

Tomoyuki Morimae

I show relations between superposition of macroscopically distinct states and entanglement. These relations lead to the important conclusion that if a state includes superposition of macroscopically distinct states, the state also includes large multipartite entanglement in terms of several measures. Such a multipartite entanglement property also suggests that if a state includes superposition of macroscopically distinct states, a measurement on a single particle drastically changes the state of macroscopically many other particles, as in the case of the $N$-qubit Greenberger- Horne-Zeilinger state.

arXiv:0912.3338•Physical Review A•Jan 25, 2010•21 citations

Entanglement analysis for macroscopic Schrödinger's Cat state

Yu‐Bo Sheng, Lan Zhou

Macroscopic entanglement, or say the Schrödinger's Cat state has attracted much attention for a long time. Recently, the first theoretical work of Fröwis and Dür ( Phys. Rev. Lett. , 106 (2011) 110402) and the first experiment of Lu et al. ( Nat. Photon. , 8 (2014) 364) both showed that, a new type of Schrödinger's Cat state, the logic-qubit entanglement (concatenated Greenberger-Horne-Zeilinger (C-GHZ) state) is immune and robust to the noise, and is possible to be applied in future large-scale quantum networks. In this paper, we describe a protocol of entanglement analysis for this kind of Schrödinger's Cat state. Both the Bell-state type of logic-qubit entanglement and multipartite C-GHZ state can be completely distinguished. Based on the entanglement analysis, an arbitrary unknown macroscopic Schrödinger's Cat superposed state can be teleportated and we can also perform the macroscopic entanglement swapping. Our protocol shows that it is possible to realize long-distance quantum communication and large-scale quantum network based on logic-qubit entanglement.

Europhysics Letters (EPL)•Feb 1, 2015•25 citations

Robustness of multipartite entanglement under collisional decoherence

Yee‐Chia Yeo

The collision model of Ziman et al. was considered and the robustness of N -qubit Greenberger-Horne-Zeilinger (GHZ), W, and linear cluster states were studied. Our results show that N -qubit entanglement of GHZ states would be extremely fragile under collisional decoherence, and that of W states could be more robust than of linear cluster states.

Optics and Spectroscopy•Aug 1, 2007•3 citations

Macroscopic Greenberger-Horne-Zeilinger and W states in flux qubits

Mun Dae Kim, Sam Young Cho

We investigate two types of genuine three-qubit entanglement, known as the Greenberger-Horne-Zeilinger (GHZ) and $W$ states, in a macroscopic quantum system. Superconducting flux qubits are theoretically considered in order to generate such states. A phase coupling is proposed to offer enough strength of interactions between qubits. While an excited state can be the $W$ state, the GHZ state is formed at the ground state of the three flux qubits. The GHZ and $W$ states are shown to be robust against external flux fluctuations for feasible experimental realizations.

arXiv:0705.3991•Physical Review B•Mar 26, 2008•26 citations
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.
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.
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.
I show relations between superposition of macroscopically distinct states and entanglement. These relations lead to the important conclusion that if a state includes superposition of macroscopically distinct states, the state also includes large multipartite entanglement in terms of several measures. Such a multipartite entanglement property also suggests that if a state includes superposition of macroscopically distinct states, a measurement on a single particle drastically changes the state of macroscopically many other particles, as in the case of the NNN-qubit Greenberger- Horne-Zeilinger state.
Macroscopic entanglement, or say the Schrödinger's Cat state has attracted much attention for a long time. Recently, the first theoretical work of Fröwis and Dür ( Phys. Rev. Lett. , 106 (2011) 110402) and the first experiment of Lu et al. ( Nat. Photon. , 8 (2014) 364) both showed that, a new type of Schrödinger's Cat state, the logic-qubit entanglement (concatenated Greenberger-Horne-Zeilinger (C-GHZ) state) is immune and robust to the noise, and is possible to be applied in future large-scale quantum networks. In this paper, we describe a protocol of entanglement analysis for this kind of Schrödinger's Cat state. Both the Bell-state type of logic-qubit entanglement and multipartite C-GHZ state can be completely distinguished. Based on the entanglement analysis, an arbitrary unknown macroscopic Schrödinger's Cat superposed state can be teleportated and we can also perform the macroscopic entanglement swapping. Our protocol shows that it is possible to realize long-distance quantum communication and large-scale quantum network based on logic-qubit entanglement.
We investigate two types of genuine three-qubit entanglement, known as the Greenberger-Horne-Zeilinger (GHZ) and WWW states, in a macroscopic quantum system. Superconducting flux qubits are theoretically considered in order to generate such states. A phase coupling is proposed to offer enough strength of interactions between qubits. While an excited state can be the WWW state, the GHZ state is formed at the ground state of the three flux qubits. The GHZ and WWW states are shown to be robust against external flux fluctuations for feasible experimental realizations.