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Creation of a six-atom ‘Schrödinger cat’ state

Abstract

Among the classes of highly entangled states of multiple quantum systems, the so-called ‘Schrödinger cat’ states are particularly useful. Cat states are equal superpositions of two maximally different quantum states. They are a fundamental resource in fault-tolerant quantum computing1,2,3 and quantum communication, where they can enable protocols such as open-destination teleportation4 and secret sharing5. They play a role in fundamental tests of quantum mechanics6 and enable improved signal-to-noise ratios in interferometry7. Cat states are very sensitive to decoherence, and as a result their preparation is challenging and can serve as a demonstration of good quantum control. Here we report the creation of cat states of up to six atomic qubits. Each qubit's state space is defined by two hyperfine ground states of a beryllium ion; the cat state corresponds to an entangled equal superposition of all the atoms in one hyperfine state and all atoms in the other hyperfine state. In our experiments, the cat states are prepared in a three-step process, irrespective of the number of entangled atoms. Together with entangled states of a different class created in Innsbruck8, this work represents the current state-of-the-art for large entangled states in any qubit system.

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Figure 1: Histogram and residuals of the |6Cat〉.
Figure 2: Coherences of all prepared cat states.

References

  1. Shor, P. W. in Proc. 37th Symp. on the Foundations of Computer Science (FOCS) 56–65 (IEEE Press, Los Alamitos, California, 1996)

    Google Scholar 

  2. Steane, A. M. & Ibinson, B. Fault-tolerant logical gate networks for css codes. Preprint at http://arxiv.org/quant-ph/0311014 (2003).

  3. Knill, E. Quantum computing with realistically noisy devices. Nature 434, 39–44 (2005)

    ADS  CAS  Article  Google Scholar 

  4. Zhao, Z. et al. Experimental demonstration of five-photon entanglement and open-destination teleportation. Nature 430, 54–58 (2004)

    ADS  CAS  Article  Google Scholar 

  5. Hillery, M., Buzek, V. & Berthiaume, A. Quantum secret sharing. Phys. Rev. A 59, 1829–1834 (1999)

    ADS  MathSciNet  CAS  Article  Google Scholar 

  6. Greenberger, D. M., Horne, M., Shimony, A. & Zeilinger, A. Bell's theorem without inequalities. Am. J. Phys. 58, 1131–1143 (1990)

    ADS  MathSciNet  Article  Google Scholar 

  7. Leibfried, D. et al. Toward Heisenberg-limited spectroscopy with multiparticle entangled states. Science 304, 1476–1478 (2004)

    ADS  CAS  Article  Google Scholar 

  8. Häffner, H. et al. Scalable multi-particle entanglement of trapped ions. Nature doi:10.1038/nature04279 (this issue)

  9. Cirac, J. & Zoller, P. Quantum computations with cold trapped ions. Phys. Rev. Lett. 74, 4091–4094 (1995)

    ADS  CAS  Article  Google Scholar 

  10. DiVincenzo, D. The physical implementation of quantum computation. Fortschr. Phys. 48, 771–783 (2000)

    Article  Google Scholar 

  11. Schrödinger, E. Die Gegenwärtige Situation in der Quantenmechanik. Naturwissenschaften 23, 807–812; 823–828; 844–849 (1935)

    ADS  Article  Google Scholar 

  12. Gottesman, D. & Chuang, I. L. Demonstrating the viability of universal quantum computation using teleportation and single-qubit operations. Nature 402, 390–393 (1999)

    ADS  CAS  Article  Google Scholar 

  13. Knill, E., Laflamme, R., Martinez, R. & Tseng, C.-H. An algorithmic benchmark for quantum information processing. Nature 404, 368–370 (2000)

    ADS  CAS  Article  Google Scholar 

  14. Leibfried, D. et al. Experimental demonstration of a robust, high-fidelity geometric two ion-qubit phase gate. Nature 422, 412–415 (2003)

    ADS  CAS  Article  Google Scholar 

  15. Sackett, C. A. et al. Experimental entanglement of four particles. Nature 404, 256–259 (2000)

    ADS  CAS  Article  Google Scholar 

  16. Bennett, C. H., Popescu, S., Röhrlich, D., Smolin, J. A. & Thapliyal, A. V. Exact and asymptotic measures of multipartite pure state entanglement. Phys. Rev. A 63, 012307 (2001)

    ADS  Article  Google Scholar 

  17. Bennett, C. H., Bernstein, J. J., Popescu, S. & Schumacher, B. Concentrating partial entanglement by local operations. Phys. Rev. A 53, 2046–2052 (1996)

    ADS  CAS  Article  Google Scholar 

  18. Dür, W., Vidal, G. & Cirac, J. I. Three qubits can be entangled in two inequivalent ways. Phys. Rev. A 62, 062314 (2000)

    ADS  MathSciNet  Article  Google Scholar 

  19. Lewenstein, M., Kraus, B., Cirac, J. I. & Horodecki, P. Optimization of entanglement witnesses. Phys, Rev. A 62, 052310 (2000)

    ADS  Article  Google Scholar 

  20. Dür, W., Aschauer, H. & Briegel, H.-J. Multiparticle entanglement purification for graph states. Phys. Rev. Lett. 91, 107903 (2003)

    ADS  MathSciNet  Article  Google Scholar 

  21. Dür, W. & Cirac, J. I. Multiparticle entanglement and its experimental detection. J. Phys. A 34, 6837–6850 (2001)

    ADS  MathSciNet  Article  Google Scholar 

  22. Rowe, M. A. et al. Transport of quantum states and separation of ions in a dual RF ion trap. Quant. Inform. Comput. 2, 257–271 (2002)

    CAS  MATH  Google Scholar 

  23. King, B. E. et al. Cooling the collective motion of trapped ions to initialize a quantum register. Phys. Rev. Lett. 81, 1525–1528 (1998)

    ADS  CAS  Article  Google Scholar 

  24. Freeman, R. Spin Choreography (Oxford Univ. Press, Oxford, UK, 1998)

    Google Scholar 

  25. Ozeri, R. et al. Hyperfine coherence in the presence of spontaneous photon scattering. Phys. Rev. Lett. 95, 030403 (2005)

    ADS  CAS  Article  Google Scholar 

  26. Langer, C. et al. Long-lived qubit memory using atomic ions. Phys. Rev. Lett. 95, 060502 (2005)

    ADS  CAS  Article  Google Scholar 

  27. Kielpinski, D. et al. A decoherence-free quantum memory using trapped ions. Science 291, 1013–1015 (2001)

    ADS  CAS  Article  Google Scholar 

  28. Bacon, D. M. Decoherence, Control and Symmetry in Quantum Computers. PhD thesis, Ch. 10 Univ. California, Berkeley (2001); http://arxiv.org/quant-ph/0305025 (2003).

  29. Efron, B. & Tibshirani, R. J. An Introduction to the Bootstrap (Chapman & Hall, New York, 1993)

    Book  Google Scholar 

Download references

Acknowledgements

This work was supported by the US National Security Agency (NSA) and Advanced Research and Development Activity (ARDA), by the Department of Defence Multidisciplinary University Research Initiative (MURI) programme administered by the Office of Naval Research and by NIST. We thank S. Glancy and J. Bollinger for comments on the manuscript. This paper is a contribution by the National Institute of Standards and Technology and not subject to US copyright.

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Correspondence to D. Leibfried.

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Leibfried, D., Knill, E., Seidelin, S. et al. Creation of a six-atom ‘Schrödinger cat’ state. Nature 438, 639–642 (2005). https://doi.org/10.1038/nature04251

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