Protecting entanglement from decoherence using weak measurement and quantum measurement reversal

Journal name:
Nature Physics
Volume:
8,
Pages:
117–120
Year published:
DOI:
doi:10.1038/nphys2178
Received
Accepted
Published online

Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence1. For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death2, 3. Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing4, quantum cryptography5, quantum teleportation6, 7, 8 and quantum metrology9. Here, we propose and demonstrate a scheme to protect entanglement from decoherence. Our entanglement protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death.

At a glance

Figures

  1. Scheme for protecting entanglement from decoherence using weak measurement and quantum measurement reversal.
    Figure 1: Scheme for protecting entanglement from decoherence using weak measurement and quantum measurement reversal.

    a, Owing to decoherence D1 and D2 in the quantum channels, Bob and Charlie end up sharing the quantum state ρd, which is either less entangled than |ϕright fence or not entangled at all owing to ESD. b, Protecting entanglement from decoherence using weak measurement and quantum measurement reversal. Alice first carries out weak measurement (Mwk) on |ϕright fence before distribution. Bob and Charlie, on receiving the qubits, carry out reversing measurement (Mrev). The resulting shared quantum state ρrcan be made as close to the original |ϕright fence by choosing {p1,p2} and {pr1,pr2} properly.

  2. Theoretical estimation of concurrence change as functions of decoherence and weak measurement.
    Figure 2: Theoretical estimation of concurrence change as functions of decoherence and weak measurement.

    The two quantum channels have different decoherence D1 and D2. ad, Plots for the maximally entangled state |ϕright fence (|α|=|β|) (a,b) and for the non-maximally entangled state |ϕright fence (|α|<|β| with |α|=0.42) (c,d). Entanglement degradation due to decoherence is shown in a and c. Weak measurement with strength p1 and p2 and the optimal reversing measurement can circumvent decoherence as shown in b and d. Plots b and d are for D1=0.6 and D2=0.8. The horizontal planes represent zero concurrence. Note that c shows ESD and d shows that even ESD-causing decoherence can be circumvented with weak measurement of sufficient strength and corresponding optimal reversing measurement.

  3. Schematic of the experiment.
    Figure 3: Schematic of the experiment.

    The initial two-qubit state |ϕright fence is prepared with the two-photon polarization state. Weak measurement (Mwk) and the optimal reversing measurement (Mrev) are carried out on the polarization qubit using Brewster-angle glass plates (BPs) and half-wave plates24 (HWPs). Amplitude-damping decoherence is introduced to the polarization qubit using an interferometer26. See Methods for details.

  4. Experimental data for protecting entanglement from decoherence using weak measurement and quantum measurement reversal.
    Figure 4: Experimental data for protecting entanglement from decoherence using weak measurement and quantum measurement reversal.

    a, As D is increased, the state ρd loses entanglement gradually. b, Carrying out Mwk(p)and the corresponding optimal Mrev(pr) enables distribution of entanglement under strong decoherence (D=0.6). Negative values are Λd for a and Λr for b. The error bars represent the statistical error of ±1 standard deviation.

  5. The success probability as a function of weak measurement strength.
    Figure 5: The success probability as a function of weak measurement strength.

    Filled circles represent experimental data and the solid line is calculated according to equation (4).

References

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Author information

  1. These authors contributed equally to this work

    • Yong-Su Kim &
    • Jong-Chan Lee

Affiliations

  1. Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea

    • Yong-Su Kim,
    • Jong-Chan Lee,
    • Osung Kwon &
    • Yoon-Ho Kim

Contributions

Y-S.K. and J-C.L. carried out the theoretical calculations, designed and carried out the experiment, analysed data and drafted the manuscript. O.K. carried out the experiment. Y-H.K. conceived the idea, designed the experiment, analysed data, wrote the manuscript and supervised the project.

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The authors declare no competing financial interests.

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