Addressable spin control with phosphorus donor molecules

Introduction Donor atoms in silicon are attractive as the basis of a solid-state quantum computer, because they combine the long-lived quantum memory of a nuclear spin with the rapid control and strong interactions possible... [ view full abstract ]

Introduction

Donor atoms in silicon are attractive as the basis of a solid-state quantum computer, because they combine the long-lived quantum memory of a nuclear spin with the rapid control and strong interactions possible with an electron spin. We experimentally compare a single phosphorus donor atom to a molecule formed of two phosphorus donors, within a single nanoelectronic device, demonstrating a scheme for intrinsic frequency addressing of electron spin qubits. [1]

Methods & Results:

Using a scanning tunnelling microscope (STM), we perform atomic-scale hydrogen desorption lithography [2] to define the single donor and molecule, along with a single electron transistor charge readout device and electrostatic gates. The transistor and gates are formed of highly phosphorus doped silicon. We perform electron spin resonance spectroscopy and observe distinct spectra, reflecting a significantly stronger hyperfine coupling in the molecule relative to the single donor.

Through comparison to tight binding simulations [3] we use the observed hyperfine spectra as a metrology tool to gain insight about the spatial separation and orientation of the donor atoms forming the molecule, which indicates a donor layout consistent with STM images taken during fabrication.

Monitoring the spin resonances as a function of time and under different magnetic field strength provides information on the nuclear spin dynamics of the two systems.

Discussion:

Donor molecules formed by atomic precision STM lithography may allow engineering of the electron wavefunction, and in particular, control over resonance frequencies. Multiple donor molecules with distinct resonances could be fabricated as qubits in close proximity, and be intrinsically addressable without any external tuning of the qubit energies. The strong confinement potential due to the presence of multiple donor atoms should also permit the confinement of multi-electron states, necessary to implement Pauli spin blockade for high fidelity state readout in donor-based devices.

[1] Hile, S. J., et al. "Addressable electron spin resonance using donors and donor molecules in silicon."  Science Advances 4, 7, eaaq1459 (2018)

[2] Schofield, S. R., et al. "Atomically precise placement of single dopants in Si." Phys. Rev. Lett. 91, 136104 (2003) 

[3] Wang, Y., et al. "Characterizing Si: P quantum dot qubits with spin resonance techniques." Scientific reports 6: 31830 (2016)