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Generation of entanglement & suppression of decoherence in ENDOR-based quantum computing

Generation of entanglement & suppression of decoherence in ENDOR-based quantum computing. Robabeh Rahimi 1 , Akira SaiToh 2 , and Mikio Nakakara 1 1 Department of Physics, Kinki University 2 Graduate School of Engineering Science, Osaka University. Liquid state NMR Quantum Computing

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Generation of entanglement & suppression of decoherence in ENDOR-based quantum computing

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  1. Generation of entanglement & suppression of decoherence in ENDOR-based quantum computing Robabeh Rahimi1, Akira SaiToh2, and Mikio Nakakara1 1 Department of Physics, Kinki University 2 Graduate School of Engineering Science, Osaka University

  2. Liquid state NMR Quantum Computing Seems working fine Drawbacks of NMR quantum computing low spin polarization Pseudo-pure states come with some costs! • requires number of experiments, molecules • weak signal intensity Exponential !!! Sates in the current NMR experiments separable (non-entangled) IICQI'07, Kish, IRAN

  3. For NMR Quantum Computing Higher nuclear spin polarizations are requires • Directly: lowering the temperature; mK required! increasing the magnetic field; current technology • Indirectly: parahydrogen molecule; a large number of qubits dynamic nuclear polarization (DNP) Spin polarization is transferred from electron spins, withhigh spin polarization, to the nuclear spins, withlow spin polarization. IICQI'07, Kish, IRAN

  4. Electron spin bus systems for quantum computing Solid state quantum computing with a bus spin, an electron spin, coupled to client qubits, many nuclear spins.* solid state can be cooled to low temperature with an available high magnetic field quantum limit can be achieved * M. Mehring, J. Mende, Phys. Rev. A 73, 052303 (2006) IICQI'07, Kish, IRAN

  5. ENDOR; Electron Nuclear DOuble Resonance NMR in paramagnetic entities Magnetic Resonasnce Technology: ENDOR = ESR＋ NMR High sensitivity (～101-2 GHz) High resolution (～1 kHz) Pulsed ENDOR electron-nuclear spin manipulation technology high sensitivity & high polarization from ESR high resolution & nuclear selectivity from NMR IICQI'07, Kish, IRAN

  6. Liq. He Cryostat with a Gas-Flow Controller Pulse Programmer Pulse Former TWTA Detector  9.6 GHz MW OSC. 1 kW High-Speed Digital Oscilloscope 8 channel ～ ENDOR Probehead (Dielectric Resonator with RF Coil) Operating at liq. He Temp. Water-cooling Electromagnet(-1.5~1.5 T) RF Generator RF Amplifier Nd:YAG Laser 50 Hz, 90 mJ (at 532 nm) 1064/532/355/266 nm Two Direct Digital Synthesizers 300 W, 0.25 150 MHz 500 W, 0.30 35 MHz 1000 W, 0.01 250 MHz Block Diagram of Pulsed QC-ENDOR Setup X-band ( 10 GHz) Version: IICQI'07, Kish, IRAN

  7. Pulse Electron Multiple Resonance SpectrometersESR/ENDOR/ELDOR IICQI'07, Kish, IRAN

  8. (a) (c) (b) RF MW (a) (c) (b) 2 2 2 1 1 1 w12 w12 w12 w24 w24 w24 3 w34 3 w34 3 w34 4 4 4 Entanglement & ENDOR • Pseudo-pure state entanglement*: • *Mehring et al., PRL.90, 153001(2003) IICQI'07, Kish, IRAN

  9. RF1 RF2 RF2 2 echo 1 w12 MW MW MW w13 w24 3 w34 4 ESR ENDOR ENDOR quantum computing (Pseudo-)Entanglement IICQI'07, Kish, IRAN

  10. B0/T RF1/MHz RF2/MHz A 1.201028 w13 22.777 w34 79.757 w12 B 1.198898 w24 22.701 w34 79.699 w12 2 C 1.198898 w24 79.699 w12 22.701 w34 1 |1 − 2 | w12 |1 + 2| w13 w24 |2| |1| 3 w34 1 = -5.2 MHz 2 = 1.0 MHz 4 ESR ENDOR ENDOR quantum computing (Pseudo-)Entanglement Malonyl Q-band IICQI'07, Kish, IRAN

  11. 1 = -5.2 MHz 2 = 1.0 MHz S IN IH |1| B0 = 1. 2044T |1 + 2| |1 − 2 | |2| B0 = 1.2066T ENDOR quantum computing (Pseudo-)Entanglement DPNO Q-band IICQI'07, Kish, IRAN

  12. Decoherence electron spin with very short decoherence time Spin-lattice relaxation time, T1@10K, saturation recovery Spin-spin relaxation time, T2@10 K , two pulse echo decay * at 20 K R. Rahimi, PhD thesis, quant-ph/0609063 IICQI'07, Kish, IRAN

  13. A conventional model of a spin-boson system On-resonance bosons, if dissipation is ignored, oscillation is found rather than a decay A dissipative model of a spin-boson system IICQI'07, Kish, IRAN

  14. Spin system Hamiltonian Boson system Hamiltonian Spin-boson coupling For a bosonic mode in resonance with the spin System study IICQI'07, Kish, IRAN

  15. the original density operator (a) Without polarization transfer is the reduced density operator of the electron spin of the original state (b) With polarization transfer IICQI'07, Kish, IRAN

  16. the total entangling operation Q-band ENDOR; 35 GHz IICQI'07, Kish, IRAN

  17. is a map A dissipative noise model IICQI'07, Kish, IRAN

  18. a Hamiltonian of bang-bang pulses is a duty ratio Decoherence control IICQI'07, Kish, IRAN

  19. at time Time evolution IICQI'07, Kish, IRAN

  20. Case without prior polarization transfer IICQI'07, Kish, IRAN

  21. Case without prior polarization transfer Wipe effect IICQI'07, Kish, IRAN

  22. Case with prior polarization transfer IICQI'07, Kish, IRAN

  23. Case with prior polarization transfer Wipe effect IICQI'07, Kish, IRAN

  24. Conclusion • For an electron spin bus system, entanglement is achieved under milder experimental conditions. • Decoherence control for an electron spin bus system is rather more challenging. • If the number of qubits is small, we find some regions of parameters, not much far from the currently accessible region of magnetic spectroscopy technology, where the quantum state can be stable. • - A high probability of dissipation of bosons result in slow decoherence, quantum wipe effect. IICQI'07, Kish, IRAN

  25. Takeji Takui (Osaka City Univ.) Mikio Nakahara (Kinki Univ.) Akira SaiToh (Osaka Univ.) Kazunobu Sato (Osaka City Univ.) Masahiro Kitagawa (Osaka Univ.) work done by S. Nishida, K. Toyota, D. Shiomi, Y. Morita,A. Ueda, S. Suzuki, K. Nakasuji (Osaka City Univ.) K. Furukawa, T. Nakamura (IMS) H. Hara, P. Carl, P. Höfer (Bruker Biospin Co.) RR is supported by Sasakawa scientific research grant from the Japan Science Society IICQI'07, Kish, IRAN

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