Coherent Storage of Photoexcited Triplet States UsingSi29Nuclear Spins in Silicon

Abstract

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the ms=±1 sub-levels differ significantly from that of the ms=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ∼100% electron spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor 29 Si nuclear spin. We measure the coherence time of the 29 Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance.PACS numbers: 71.55.Cn, 76.70.Dx, 03.67.Lx Nuclear spins in solids are promising candidates for quantum bits (qubits) as their weak coupling to the environment often leads to very long spin coherence times [1][2][3][4]. However, performing fast manipulation and controlling interaction between nuclear spin qubits is often more challenging than in other, more engineered, quantum systems [5][6][7]. The use of an optically driven mediator spin has been suggested as a way to control coupling between donor electron spins in silicon: the donor spins exhibit weak direct coupling, but mutually couple through the optically excited state of the mediator [8]. Such ideas could similarly be applied to couple nuclear spins, and, if the mediator spin is a photo-excited triplet with a spinzero single ground state, it would have the added advantage that it avoids long-term impact on the nuclear spin coherence [9][10][11].Photoexcited triplets are optically-generated electron spins (S = 1) which often exhibit large (positive or negative) spin polarization, thanks to preferential population of each of the triplet sub-levels following intersystem crossing and/or the differing decay rates of these sublevels to the ground singlet state [12,13]. Nuclear spins, in contrast, have weak thermal spin polarization at experimentally accessible conditions, due to its small magnetic moment. Highly polarized electron spin triplets can be used to polarize surrounding nuclear spins, through continuous wave microwave illumination (under processes termed dynamic nuclear polarization) [14,15], or using microwave pulses [16]. Triplet states can also be used to mediate entanglement between mutually-coupled nuclear spins [9], on timescales much faster than their intrinsic dipolar coupling [17].Oxygen-vacancy (O-V ) complexes can be formed in silicon by electron beam or γ-ray irradiation of oxygen-rich silicon crystals [18,19], and can be excited to the triplet state (termed an SL1 center,) using illumination of above band gap light [20]. Magnetic resonance studies including electron paramagnetic resonance (EPR), electrically or optically detected magnetic resonance, spin dependent recombination and electrically-detected cross relaxation [20][21][22][23][24][25] have revealed that the SL1 has ...

Isotope engineering of silicon and diamond for quantum computing and sensing applications

“…This allowed a very large, most likely >90%, polarization of the 29 Si nuclear spins. [83] Taking the advantages of the long coherence time and the absence of inhomogeneous broadening in the phosphorus ESR and electron nuclear double resonance (ENDOR) lines for the phosphorus donors in isotopically enriched IKZ bulk 28 Si, the international collaboration led by John Morton (formally at University of Oxford and presently at University College London) succeeded in a series of proof-of-concept two-qubit experiments. Here, one qubit was the electron spin of the phosphorus atom and the other was the 31 P nuclear spin.…”

“…[87] In parallel, the Keio-UCL collaboration demonstrated coherent transfer between the electron spin states and 29 Si nuclear spin states for two-qubit operations. [83] These accomplishments, obtained with ensembles of donor electron spins, donor nuclear spins, and 29 Si nuclear spins in silicon formed the foundation of single-bit quantum information processing (QIP) in silicon, which will be discussed in the next section.…”

Spin-dependent recombination involving oxygen-vacancy complexes in silicon

“…10,11 In particular, the SL1 center has been used to demonstrate a coherent state transfer between electron and nuclear spins in silicon. 12 The SL1 center has been extensively studied by continuous-wave (cw) and pulsed electron paramagnetic resonance (EPR) methods. 13,14 Read-out of the SL1 spin state is also possible by electric means using a spindependent recombination process involving the SL1 center.…”

Hyperfine spin qubits in irradiated malonic acid: heat-bath algorithmic cooling

“…The results indicate that experimental cooling of nuclear spins beyond the thermal electron spin temperature, while challenging, is feasible in this quantum processor. These techniques can be applied to malonic acid or similar radical molecules at very low temperatures, or to optically polarizable systems such as NV centers in diamond [28][29][30] or molecules with photoexcited triplet states [31] at room temperature, to reach the nuclear spin polarizations of order unity useful for QEC.…”