Driven coherent oscillations of a single electron spin in a quantum dot

Abstract

The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuouswave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits.The use of quantum mechanical superposition states and entanglement in a computer can theoretically solve important mathematical and physical problems much faster than classical computers 1,2 . However, the realization of such a quantum computer represents a formidable challenge, because it requires fast and precise control of fragile quantum states. The prospects for accurate quantum control in a scalable system are thus being explored in a rich variety of physical systems, ranging from nuclear magnetic resonance and ion traps to superconducting devices 3 .Electron spin states were identified early on as an attractive realization of a quantum bit 4 , because they are relatively robust against decoherence (uncontrolled interactions with the environment). Advances in the field of semiconductor quantum dots have made this system very fruitful as a host for the electron spin. Since Loss and DiVincenzo's proposal 5 on electron spin qubits in quantum dots in 1998, many of the elements necessary for quantum computation have been realized experimentally. It is now routine to isolate with certainty a single electron in each of two coupled quantum dots [6][7][8][9] . The spin of this electron can be reliably initialized to the ground state, spin-up, via optical pumping 10 or by thermal equilibration at sufficiently low temperatures and strong static magnetic fields (for example, T=100 mK and B ext =1 T). The spin states are also very long-lived, with relaxation times of the order of milliseconds [11][12][13] .Furthermore, a lower bound on the spin coherence time exceeding 1 µs was established, using spin-echo techniques on a two-electron system 14 . These long relaxation and coherence times are possible in part because the magnetic moment of a single 1 electron spin is so weak. On the other hand, this property makes read-out and manipulation of single spins particularly challenging. By combining spin-to-charge conversion with real-time single-charge detection [15][16][17] , it has nevertheless been possible to accomplish single-shot read-out of spin states in a qu...

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

“…Seminal efforts are underway in the control of artificial quantum systems, that can be made to emulate the underlying Fermi-Hubbard models [5, 6, 7, 8,9,10,11]. Electrostatically confined conduction band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical pure-state initialisation and readily adhere to an engineerable Fermi-Hubbard Hamiltonian [12,13,14,15,16,17,18,19,20,21,22,23]. Until now, however, the substantial electrostatic disorder inherent to solid state has made attempts at emulating Fermi-Hubbard physics on solid-state platforms few and far between [24,25].…”

“…Coherent evolution of excitations in charge and spin can span many sites, as, contrary to what might be expected, dissipation and decoherence rates induced by electromagnetic noise can be made > 20 times smaller than the relevant coupling energies [20,22,23]. Furthermore, local control and read-out of both charge and spin degrees of freedom have become matured areas of research, given the large ongoing effort of using quantum dots as a platform for quantum information processing [17,18,19,20,21,22,23]. In particular, excellent control of small on-site energy differences [20,28] or tunnel couplings [22,23] has been shown at specific values of electron filling and tuning.…”

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

“…[2][3][4] In GaAs-based qubits, which are the state of the art, the essential gate operations 1, 5,6 for quantum computation 7,8 have been demonstrated. [9][10][11][12][13][14][15][16][17][18] But GaAs possesses a serious handicap for coherent spin manipulations-the nuclear spins. 19,20 Controlling this source of decoherence is of major interest and an active field of research.…”

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

“…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. 8 In addition to these fascinating technological applications, quantum dots constitute a unique well-controllable system to study fundamental physical aspects of transport in the strong Coulomb-correlated regime and its interplay with spin-dependent effects.…”