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Why Diamond? Why Diamond Photonic Crystal?
Diamond is an extraordinary material. It is well known for exceptional mechanical hardness, thermal conductivity, optical transparency, and phenomenal chemical resistance. However, all these well renowned characteristics might obscure distinguished quantum mechanical properties of a special diamond luminescent defect, called the Nitrogen Vacancy (NV) center. This center when combined with scalable photonic crystal architecture can lead to room-temperature operating Quantum Information Technology (QIT). The first step in the QIT realization is demonstration of atom-photon interaction (single NV center strongly coupled to a high-Q cavity). This is a prime focus of our research. In this brief resume we would like to address two questions: "Why Diamond?", and "Why Diamond Photonic Crystals?" |
Diamond is Forever,
even in QIT!
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Figure 1: Diamond NV center. (a) The Schematics of the NV lattice arrangement10. (b) The energy levels structure of the NV optical centre in diamond.
The NV center consists of a nitrogen atom substituting a carbon atom plus a nearest neighbor vacancy (see Fig. 1a). Its ground state and excited state are forming an electron spin triplet with 3A and 3E symmetries1. Due to the spin-spin interaction in the diamond crystal, the ground state is split into (ms=0) and (ms=±1) sublevels2. The optical transition between the ms=0 ground and excited states has an energy of 1.945eV (λ0=637.3nm). This transition displays high quantum efficiency (allowing single defect spectroscopy3), spin selectivity and rapid system spin polarization the into the ground state4. Among other important properties of the center are:
· Long decoherence times: T1 ~1s at low temperature and 1ms at room temperature 5, T2~30 microseconds5,6.
· Optical transition tuning by Stark shift7.
· The optical center is especially stable (no photo bleaching is observed8).
Most importantly, the NV center is the only system, allowing spin manipulation and read-out at room temperature11.
Several basic elements of diamond Quantum Computing have already been demonstrated: two-qubit conditional quantum gate9 (using NV center neighboring a 13C atom) and coherent coupling between NV center and a neighbor N atom10. These demonstrations rely on the dipolar coupling between spins, which limits the interaction to ~10nm distance10. Therefore, a true-multi NV center operation in this approach is extremely challenging. To solve this problem, we suggest an architecture in which each NV center is insulated from the environment both "electrically" via the ultra-pure substrate (separating him from the other NV centers) and optically (by locating each center in a high-Q cavity). In this way, the center is being strongly coupled to its own cavity mode, while decoherence is minimized, thus leading to the long operation times. The interaction between many centers or addressing each one of them is performed by photons, while the control over this interaction and the resulting decoherence is via a Q switching mechanism12.
Eventually, when the advantages of diamond photonic crystal QIT are discussed, it is a high time to remind the challenges in its realization. These are nascent fabrication technology, and low-ε photonic crystal design. Both of these topics will be addressed in next communications on this site.
1 "Properties and Growth of Diamond", edited by G. Davies, INSPEC, London, (1994).
2 J.P. Harrison et. al, M.J. Sellars and N.B. Manson, "Optical spin Polarization of the N-V centre in diamond", J. Lumin. 107, 245, (2004).
3 A. Gruber, A. Drabenstedt, C. Tietz, L. Fleury, J. Wrachtrup, and C. von Borczyskowski, "Scanning Confocal Optical Microscopy and Magnetic Resonance on Single Defect Centers", Science, 276, 2012, (1997).
4 E. van Oort, P. Stroomer, and M. Glasbeek, "Low-field optically detected magnetic resonance of a coupled triplet-doublet defect pair in diamond ", Phys. Rev. B 42, 8605 (1990).
5 F. Jelezko, T. Gaebel, I. Popa, A. Gruber, and J. Wrachtrup, "Observation of Coherent Oscillations in a Single Electron Spin", Phys. Rev. Lett. 92, 076401 (2004).
6 T. A. Kennedy, F.T. Charnock, J. S. Colton, J. E. Butler, R.C. Linares, and P. J. Doering," Single-qubit operations with the nitrogen-vacancy center in diamond" Phys. Status Solidi (b), 233, 416 (2002).
7 Ph. Tamarat, T. Gaebel, J.R. Rabeau, M. Khan, A.D. Greentree, H. Wilson, L.C.L. Hollenberg, S. Prawer, P.R. Hemmer, F. Jelezko, and J. Wrachtrup, "Stark Shift Control of Single Optical Centers in Diamond", Phys. Rev. Lett. 97 (8), 083002 (2006).
8 J. Wrachtrup and F. Jelezko, Processing quantum information in diamond, J. Phys.: Condens. Matter 18, S807, (2006).
9 F. Jelezko, T. Gaebel, I. Popa, M. Domhan, A. Gruber, and J.Wrachtrup, "Observation of Coherent Oscillation of a Single Nuclear Spin and Realization of a Two-Qubit Conditional Quantum Gate", Phys. Rev. Lett. 97 (8), 083002 (2006).
10 T. Gaebel, M. Domhan, I. Popa, C. Wittmann, P. Neumann, F. Jelezko, J. R. Rabeau, N. Stavrias, A. D. Greentree, S. Prawer, J. Meijer, J. Twamley, P. R. Hemmer and J. Wrachtrup, "Room-temperature coherent coupling of single spins in diamond", Nature Physics, 2, 408,(2006).
11 A. P. Nizovtsev, S. Y. Kilin, F. Jelezko, I. Popa, A. Gruber, C. Tietz, J. Wrachtrup, "Spin-selective low temperature spectroscopy on single molecules with a triplet-triplet optical transition: Application to the NV defect center in diamond", Optics and Spectroscopy, 94, 848, (2003).
12 A. D. Greentre, J. Salzman, S. Prawer, and L. C. Hollenberg, "Quantum gate for Q-switching photonic band-gap cavities containing two level atoms" Phys. Rev. A73, 013818 (2006). |
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