Controlled tunneling-induced dephasing of Rabi rotations for high-fidelity hole spin initialization

Abstract

We report the sub-picosecond initialization of a single heavy hole spin in a self-assembled quantum dot with > 98.5% fidelity and without external magnetic field. Using an optically addressable charge and spin storage device we tailor the relative electron and hole tunneling escape timescales from the dot and simultaneously achieve high-fidelity initialization, long hole storage times and high efficiency readout via a photocurrent signal. We measure electric field-dependent Rabi oscillations of the neutral and charged exciton transitions in the ultrafast tunneling regime and demonstrate that tunneling induced dephasing (TID) of excitonic Rabi rotations is the major source for the intensity damping of Rabi oscillations in the low Rabi frequency, low temperature regime. Our results are in very good quantitative agreement with quantum-optical simulations revealing that TID can be used to precisely measure tunneling escape times and extract changes in the Coulomb binding energies for different charge configurations of the quantum dot. Finally, we demonstrate that for sub-picosecond electron tunneling escape TID of a coherently driven exciton transition facilitates ultrafast hole spin initialization with near-unity fidelity.

Generation of Non‐Classical Light Using Semiconductor Quantum Dots

“…Figure 4e). After initializing a spin either by spin pumping or tunneling ionization the system can be put in an excited state from where it relaxes to a coherent superposition of the two ground states which is entangled with the energy and polarization of the emitted photon. In addition to the demonstration of spin–photon entanglement with over 90% fidelity, the teleportation of a photon polarization into the QD spin and the entanglement between remote electron spins and hole spins has been demonstrated.…”

Electrical control of quantum-dot fine-structure splitting for high-fidelity hole spin initialization

“…For example, when F = 48.1 kV/cm (V b = −302.6 mV) a theoretical fidelity of >99.99 999% (or, equivalently, a loss in fidelity of <10 −7 ) is predicted [42] for the QD used here, while the initialization time and hole lifetime are 0.6 and 474.5 ps, respectively. Although the above hole lifetime is relatively short for achieving efficient spin storage [12,25] (which is the reason we refrained from presenting hole spin initialization measurements here), this may be easily resolved by using techniques, such as postgrowth thermal annealing [29], to appropriately reduce the as-grown inhomogeneous δ FS of the QD ensemble. This would allow the electric field required to achieve near-zero δ FS to be lower where hole lifetimes may be sufficiently long to allow for efficient spin storage while still meeting the requirements for speed in hole spin initialization [12].…”

“…For the practical implementation of quantum computing based on such qubits, a necessary requirement is the fast initialization of individual spins with high fidelity and within a scalable device architecture [4]. With the belief that hole spins [5][6][7][8][9][10][11][12][13][14][15][16] are at least as suitable as qubits compared to electron spins [17][18][19][20][21] due to their weak hyperfine interaction with the nuclear spin ensemble and vanishing phonon-coupled spin relaxation in the limit of a zero magnetic field and with the recent demonstration of optical coherent spin manipulation and readout without magnetic fields [22], there has been an increased interest recently [12,[23][24][25] in demonstrating fast high-fidelity hole spin initialization without magnetic fields via rapid electric-field ionization of a spinpolarized neutral exciton (X 0 ). However, the achieved fidelities using this initialization scheme have so far been limited by an intrinsic X 0 fine-structure splitting δ FS [26], which causes X 0 spin precession prior to the ionization via electron tunneling.…”

Precise measurements of the dipole moment and polarizability of the neutral exciton and positive trion in a single quantum dot

“…Virtually all protocols for the optical initialization [4][5][6][7], manipulation [8][9][10], and readout [6,11,12] of a QD spin qubit rely on intermediary exciton states in order to perform the desired quantum computing operation. A particular sequence of such protocols that has attracted much interest recently [6,7,13,14] relies on the coherent control of both the neutral exciton (X 0 ) and positive trion (X + ) states as intermediary states in order to perform initialization, manipulation, and readout of a QD hole spin qubit embedded in a photodiode device. Therefore, precise measurements of the permanent dipole moment (i.e.…”

“…fitting an appropriate theoretical model to the measured transition energies as a function of vertical electric field. A sequence of protocols [6,7,13,14] for the optical initialization, manipulation, and readout of a QD hole spin qubit embedded in a photodiode device relies on the coherent control of both X 0 and X + as intermediary states. Therefore, while QD hole spins should be more favourable as qubits compared to electron spins since their hyperfine interaction with the nuclear spin ensemble leading to decoherence is greatly suppressed [27], such precise measurements of p and β for both X 0 and X + using high-resolution PC spectroscopy are crucial for implementing these protocols with high fidelity in a QD spin-based quantum computer.…”