Single-spin readout for buried dopant semiconductor qubits

Abstract

In the design of qua ntum computer architectures that take advantage of the long coherence times of dopant nuclear and electron spins in the solid-state, singlespin detection for readout remains a crucial unsolved problem. Schemes based on adiabatically induced spin-dependent electron tunnelling between individual donor atoms, detected using a single electron transistor (SET) as an ultrasensitive electrometer, are thought to be problematic because of the low ionisaton energy of the final D − state. In this paper we analyse the adiabatic scheme in detail. We find that despite significant stabilization due to the presence of the D + , the field strengths required for the transition lead to a shortened dwell-time placing severe constraints on the SET measurement time. We therefore investigate a new method based on resonant electron transfer, which operates with much reduced field strengths. Various issues in the implementation of this method are also discussed.

Controlled phase gate for solid-state charge-qubit architectures

“…Most charge qubit schemes so far proposed implicitly rely on a fixed, always-on Coulomb interaction between qubits [6,10,15] Such schemes would necessarily require * Electronic address: sgs29@cam.ac.uk global control techniques [16][17][18], which may be problematic given the strength of the Coulomb interaction.…”

“…Furthermore, schemes compatible with present semiconductor technologies [3][4][5][6] are especially attractive because of their potential to leverage the associated industrial experience [7,8].…”

“…Such systems were amongst the first proposed for quantum computing [9] and numerous versions have evolved recently [6,[10][11][12]. We are attracted to charge-based systems for three reasons: (1) proven high-fidelity readout compatible with single-shot operations [13]; (2) potential for high-speed (∼ picosecond) operations [6]; and (3) the ability to define variable dimensionality Hilbert spaces by appropriate partitioning [14].…”

Proposal for a loophole-free test of nonlocal realism with electron spins of donors

“…The qubits are then read out with perfect efficiency and high accuracy above 99% in about 0.6 µs using optically induced spin to charge transduction [26,27,28]. The realization of the setup is within the ability of the current semiconductor fabrication technology [29,30,31], and the read-out of the single donor electron spin can be realized through resonant spin-dependent charge transfer where the resulting electron current is measurable using radio-frequency single electron transistor (rf-SET) [24,26,27,28,32].A Bell measurement of inequality of Clauser, Horne, Shimony, and Holt (CHSH) [4] comprises of three basic ingredients. First, a pair of particles entangled with each other is prepared in a repeatable starting configuration.…”

“…This leads to an experimental result that the probability of the qubit spin parallel to the SET-donor spin will be larger than that obtained with the perfect detection accuracy. The read-out of the qubit spin with the detection accuracy κ ≥ 0.99 may be possible according to [28,32]. Considering the detection accuracy κ and the detection error rate τ = 1 − κ, the violation of the CHSH inequalities B in Eq.…”