Optically programmable electron spin memory using semiconductor quantum dots

Abstract

The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.

Towards a fullerene-based quantum computer

“…It may be possible to couple the endohedral spin to a solid-state magnetic optical dipole such as nitrogen-vacancy centres in nanocrystalline diamond [24,25], which have themselves formed the basis of a QIP proposal [26] and in which a single spin has been optically measured [27]. Spin to photon conversion has also been demonstrated in InAs selfassembled quantum dots [28]. Direct optical detection of spin in N@C 60 and P@C 60 appears elusive, because the transition to the first excited state in atomic nitrogen falls far into the ultraviolet, which is beyond the capabilities of standard optics apparatus and well inside the primary absorption of the C 60 cage.…”

Hole-spin initialization and relaxation times in InAs/GaAs quantum dots

“…That is why the electron spin relaxation and decoherence sources in QDs have been intensively studied in the last few years; some more limited number of studies have centered on the hole spin. The main conclusions of these studies are that in moderate magnetic fields (1-10 T) and at low temperature, the electron T e 1 and the hole T h 1 spin-relaxation times are governed by the same mechanism, i.e., the spin-orbitmediated single-phonon scattering, [4][5][6][7][8] which leads to relatively slow relaxation times in the range of milliseconds [9][10][11][12][13] with T h 1 five or ten times smaller than T e 1 . 12 However, the electron-and hole-spin coherence times T e,h 2 have been found to be in the microsecond range up to 15 K, [14][15][16][17] and for higher temperatures T e 2 has shown a sharp decrease 16 related to the modulation by phonons of the hyperfine (hf) interaction with the random fluctuating host nuclear spins.…”

Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green’s functions

“…Spin-dependent transport in quantum dots ͑QDs͒ is a subject of intense study nowadays due to its relevance to proposed spintronic devices that encompass, for instance, the Datta-Das transistor, 1 memory devices, 2,3 and as an ultimate goal, quantum computers. 4 In particular, the recent progress in the coherent control of electron spins in quantum dots [5][6][7] has stimulated even further the research in this field for possible applications in quantum computation and quantum information processing.…”