Spin-Orbit-Mediated Manipulation of Heavy-Hole Spin Qubits in Gated Semiconductor Nanodevices

Abstract

A novel spintronic nanodevice is proposed that is capable to manipulate the single heavy hole spin state in a coherent manner. It can act as a single quantum logic gate. The heavy hole spin transformations are realized by transporting the hole around closed loops defined by metal gates deposited on top of the nanodevice. The device exploits Dresselhaus spin orbit interaction which translates the spatial motion of the hole into a rotation of the spin. The proposed quantum gate operates on sub nanosecond time scales and requires only the application of a weak static voltage which allows for addressing heavy hole spin qubit individually. Our results are supported by quantum mechanical time dependent calculations within the four band Luttinger Kohn model. There is currently great interest in studying spin related phenomena in semiconductors. On the one hand there is novel fundamental physics at the nanoscale and on the other hand one expects applications in terms of spin based quantum information processing [1,2]. Physical realization of quantum computers requires fulfillment of a number of challenging criteria [3]. A fragile quantum state has to be coherent for sufficient long time which usually requires its isolation from the environment. On the other hand it has to be externally manipulated. For these purposes, the electron spin in semiconductor quantum dots was suggested as a promising candidate [4]. There are a number of experiments in which the electron spin is initialized, manipulated, stored and read out [5][6][7][8][9][10][11].Usually spin state manipulation requires the application of microwave radiation, radio-frequency electric fields as well as magnetic fields. These methods strongly limits the possibility to address spins qubits individually. The first step towards selective control of individual single electron spins was demonstrated in recent state of the art experiments [12,13]. Electron spin manipulation was realized by means of electric fields which can be generated locally quite easily and indirectly via spin orbit interaction which couples charge and spin degrees of freedom. Electron spin control based on spin orbit effect was also proposed in some theoretical papers [14][15][16][17][18].Unfortunately, in most semiconductor quantum dots the electron spin is exposed to hyperfine interaction with nuclear spins which are present in the host material. This interaction is then the main source of electron spin decoherence in quantum dots putting a severe restriction on the possibility to realize a highly coherent electron spin qubit [19,20]. There are several appealing ideas how to deal with this type of decoherence in quantum dot systems [21]. Very promising way to eliminate or reduce the contact hyperfine interaction with the nuclear spin lattice is to use the spin state of the valence holes -a missing electron in the valence band -as a carrier of quantum information instead of electrons. Holes are described by the porbitals that vanish at a nuclear site which strongly suppresses the hyperfine conta...

Consequences of Spin-Orbit Coupling at the Single Hole Level: Spin-Flip Tunneling and the Anisotropic g Factor

“…To date, however, only partial anisotropy was demonstrated, e.g., in InAs SADs [20] and silicon nanowires [21]. Holes in GaAs are also subject to strong Dreselhaus and Rashba spin-orbit interactions, which introduce the coherent spin-flip tunneling [12,13]. In silicon DQDs these interactions are absent, leading to Pauli spin blockade [21][22][23].…”

“…Our hole device is different from the electronic system in two aspects. First, the HH in III-V materials experiences a strong spin-orbit interaction, causing the hole spin to rotate during tunneling [12,13,26]. In electronic devices this process was found to be orders of magnitude weaker [28].…”

“…The hole properties are traced to the amount of HH-LH subband mixing [12,13], which is related to the details of quantum confinement, strain, and the spin-orbit interaction. The early prediction of greatly reduced hyperfine interaction between hole and nuclear spins, and concomitant increased coherence times [14,15], were confirmed experimentally in systems with small HH-LH mixing realized as selfassembled dots (SADs) [16][17][18] or nanowires [19].…”

Insensitivity of spin dynamics to the orbital angular momentum transferred from twisted light to extended semiconductors

“…Bh, 78.20.Ls, 78.40.Fy, 42.50.Tx Light with orbital angular momentum (OAM), referred to as twisted light, is a relatively new field of research which has become increasingly popular [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] since Allen et al showed how twisted light beams can be easily generated from conventional laser beams [18]. Recently, the theoretical foundation of the optical excitation of solids and nanostructures with twisted light has been established [19][20][21][22][23][24][25][26][27], and experimental studies with twisted light on semiconductors have been carried out [28,29].One motivation for such studies is the prospect of using the large amounts of angular momentum that twisted light can carry in order to control the spin dynamics of electrons, thus adding a flexible tool to the active field of spin control [30][31][32][33][34][35][36][37][38][39]. In this context two different mechanisms need to be distinguished.…”

Maximizing the purity of a qubit evolving in an anisotropic environment

“…45,46 In addition to optical coherent control of hole spins in self-assembled quantum dots, 39,41,47,48 there are several suggestions for electrical manipulation of hole spins. [49][50][51] Such electrical control has recently been demonstrated for hole spins in III-V nanowire quantum dots, 52 and coherence times have now been measured for hole spins in Ge-Si core-shell nanowire quantum dots. 53 The very recent achievement of the few-hole regime in lateral gated double-dot devices, 54 suggests that previous highly successful measurements performed for electron spins [55][56][57][58][59][60] can now be performed for hole spins, which show promise for much longer coherence times.…”