Ultrafast Coherent Electron Spin Flip in a Modulation-Doped CdTe Quantum Well

Abstract

We report the experimental realization of coherent electron spin flip in a modulation-doped CdTe quantum well. Coherent spin rotation is realized with an off-resonant laser pulse, which induces a polarization-dependent optical Stark shift in the trion resonance. Complete electron spin flip is made possible by a laser pulse designed to avoid excessive excitations of nearby exciton resonances and minimizes detrimental many-body effects. These results demonstrate an effective approach for ultrafast optical spin control in a complex spin system.

Manipulation of ferromagnets via the spin-selective optical Stark effect

“…22 Although their Curie temperature at present is below room temperature, studying these materials can improve our understanding of novel physical phenomena that are also present in other magnets. [23][24][25] Photoinjected carriers induced by linearly polarized light with frequency slightly above the or L band edges have been shown to induce magnetization dynamics in GaMnAs. 23,26 In contrast, we focus here on excitation with frequencies below the fundamental band gap, which is dissipationless, since no free carriers are excited.…”

Quantum control of electron spins in the two-dimensional electron gas of a CdTe quantum well with a pair of Raman-resonant phase-locked laser pulses

“…1 results from individual laser pulses. This term corresponds to spin rotations induced by a DC magnetic field along the x-axis, as extensively investigated in earlier studies [7][8][9][10][11][12][13][14] . The second term in Eq.…”

“…The coherent optical interactions can also be exploited for the generation of spin-photon quantum entanglement in atomic as well as solid-state spin systems [3][4][5][6] . Optical spin control using ultrafast laser pulses has been demonstrated in various semiconductor systems [7][8][9][10][11][12][13] and also in trapped ions 14 . In these experiments, individual off-resonant laser pulses act like an effective DC magnetic field along the optical axis, inducing a spin rotation about the fixed axis.…”

High Fidelity Quantum Gates via Analytically Solvable Pulses

“…A path that excites the population in state |n resonantly to |E and returns it through a cyclic evolution will induce a minus sign to state |n . This is a familiar property of quantum systems that differentiates (pseudo)spin from spatial rotations in euclidian space, where a full 2π rotation returns the system to its starting point.Indeed, this evolution has been used in the demonstration of quantum gates of a variety of systems, including semiconductor nanostructures [3,6,11,12], trapped ions [13] and fullerene molecules [14]. This is done straightforwardly by a resonant pulse of any temporal profile.…”

“…Single qubit rotations combined with the conditional C-Z phase gate form a universal set of quantum logic gates [1]. Time dependent controls, such as lasers, are used in order to implement these prescribed unitary evolutions of the qubits.In many physical systems, such as self-assembled quantum dots [2][3][4][5] and quantum wells [6], trapped ions [7] and atoms [8], defects in solids [9], and in some cases superconducting qubits [10], auxiliary states outside the Hilbert space of the qubit are used in order to implement these gates. One advantage of using such states is that their energy splitting from the qubit states is typically orders of magnitude larger than the qubit splitting itself and thus fast operations can be achieved, since the time scales as the inverse of the energy.…”