Dynamic initialization of a carbon nuclear spinwith a coherent microwave around zero field
Koji Sato1, Yuhei Sekiguchi1, Riyo Enyo1, Yusuke Komura1, Hiroki Kano1, Ryota Kuroiwa1,Koyo Kuramitani1, Takaaki Nakamura1, Kodai Nagata1, Naoki Ishida1, and Hideo Kosaka1*
1

Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan*Corresponding author: kosaka-hideo-yp@ynu.ac.jp

Abstract: We demonstrated initialization of a 13C nuclear spin with 65% fidelity together
with initialization of a nitrogen nuclear spin with 76% fidelity under an effective zeromagnetic field with a temporal square magnetic field.
.
1. Introduction
Toward realization of quantum information technologies such as quantum repeater, quantum computer, andquantum sensor, we need to prepare quantum platform in which we can handle a large enough number ofqubits to implement quantum information processors. We have recently proposed a degenerate quantum
platform [1-3], where the logical qubits cannot be rotated with the conventional method. We havedemonstrated quantum entanglement measurement and quantum teleportation from a photon to nitrogen
nuclear spin in our quantum platform [4]. In this work, we demonstrate that our quantum platform is scalable
by showing that we can handle carbon nuclear spins together with a nitrogen nuclear spin in a nitrogenvacancy (NV) center in diamond (Fig. 1a,b).

2. Experimental setups
We used a native NV center in a high-purity type-IIa high-pressure-high-temperature grown bulk diamondwith a <001> crystal orientation (from Sumitomo electric) without any electron-beam dose or annealing. A
negatively-charged NV center located at about 10 m below the surface was found using a confocal laser
microscope. A 25-m copper wire mechanically attached to the surface of the diamond was used to apply amicrowave. An external magnetic field was applied to carefully compensate the geomagnetic field of about
0.045 mT using a permanent magnet. The NV center used in the experiment showed hyperfine splitting caused
by 14N nuclear spin and 13C nuclear spin at 2.2 MHz and 6.5 MHz, respectively. All experiments wereperformed at room temperature.
Reduction of entropy by a green laser (532 nm, 100 W) and unitary manipulation by a microwave (~2.87GHz) and a radio wave (~5 MHz) initializes the electron spin, the 14N nuclear spin and 13C nuclear spin tothe ground ms=0 state, the ground mI=0 state, and the up state, respectively. During manipulating the 13C
nuclear spin state, a temporal square magnetic field was applied. All the light beams were focused onto thesample using a 1.4 NA 100x objective lens.
3. Experimental results
After the spin states were initialized by a green laser, a microwave, and a radio wave, we checked the fidelityof initialization by Optically Detected Magnetic Resonance (ODMR).We used a temporal square magnetic
field in both initializing the spin states and checking the fidelity. We demonstrated initialization of a 13C
nuclear spin with 83% fidelity (Fig. 2a). We also demonstrated initialization of a 13C nuclear spin with 65%
fidelity together with initialization of a 14N nuclear spin with 76% fidelity under an effective zero magnetic
field with a temporal square magnetic field (Fig. 2b).
4. Acknowledgements
We thank Yuichiro Matsuzaki, Kae Nemoto, William Munro, Norikazu Mizuochi, Fedor Jelezko, and Joerg
Wrachtrup for their discussions and experimental help. This work was supported by National Institute ofInformation and Communications Technology (NICT) Quantum Repeater Project, and by Japan Society for
the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (24244044, 16H06326, 16H01052)
and Ministry of Education, Culture, Sports, Science and Technology (MEXT) as “Exploratory Challenge on
Post-K computer” (Frontiers of Basic Science: Challenging the Limits).

5. References[1] H. Kosaka and N. Niikura, Entangled Absorption of a Single Photon with a Single Spin in Diamond. Phys. Rev. Lett. 114, 053603(2015).
[2] Y. Sekiguchi et al., Geometric spin echo under zero field. Nat. Commun. 7, 11668 (2016).
[3] Y. Sekiguchi, N. Niikura, R. Kuroiwa, H. Kano, and H. Kosaka, Optical holonomic single quantum gates with a geometric spin
under a zero ﬁeld. Nat. Photon. in press (2017).
[4] S. Yang et al., High-ﬁdelity transfer and storage of photon states in a single nuclear spin. Nat. Photon. 10, 507-511 (2016).

Fig.1 (a) Nitrogen-vacancy center with carbon isotopes in diamond. (b) Concept of dynamic nuclear spin
initialization around zero magnetic field.

Fig.2 (a) ODMR spectra after (a) initialization of carbon nuclear spin into the up state and (b) initializationof carbon and nitrogen nuclear spins into the up and 0 states, respectively, at the same time.