Quantum information processing with single atoms in silicon

Seminar

A phosphorus (31P) donor in silicon is, almost literally, the equivalent of a hydrogen atom in vacuum. It possesses electron and nuclear spins 1/2 which act as natural qubits, and the host material can be isotopically purified to be almost perfectly free of any nuclear spin carrying isotopes, ensuring extraordinary coherence times. Silicon – the semiconductor underpinning the whole modern computing era – is also the perfect material for quantum information hardware. I will present the current state-of-the-art in silicon quantum information technologies. Both the electron [1] and the nuclear [2] spin of a single 31P atom can be read out in single-shot [3] with high fidelity, through a nanoelectronic device compatible with standard semiconductor fabrication. High-frequency microwave [4] pulses can be used to prepare arbitrary quantum states of the spin qubits, with fidelity in excess of 99.9%. And our experiment on the 31P nucleus has established the record coherence time (35 seconds) for any single qubit in the solid state [5], by making use of an isotopically enriched 28Si epilayer. The exceptional quality of these qubits has allowed us to perform a variety of more complex quantum experiments. I will showcase an overview of our most recent results on the electrical control of a spin in a continuous microwave field [6], the violation of Bell’s inequality in the electron-nuclear two-qubit system [7], a nuclear spin quantum memory [8], and the operation of a spin qubit in the noisy environment of a cryogen-free dilution refrigerator [9]. In the last part of my talk, I will focus on the microwave-dressed, donor-bound electron in silicon. In our work we investigate the properties of the dressed spin and probe its potential for the use as quantum bit in scalable architectures [10]. We observe a Mollow triplet in the excitation spectrum, and demonstrate full two-axis control of the driven qubit in the dressed frame with a number of different control methods. We measure coherence times of T2* = 2.4 ms and T2Hahn = 9 ms, one order of magnitude longer than those of the undressed qubit. [1] J. Pla et al., Nature 489, 541 (2012) [2] J. Pla et al., Nature 496, 334 (2013) [3] A. Morello et al., Nature 467, 687 (2010) [4] J. Dehollain et al., Nanotechnology 24, 015202 (2013) [5] J. T. Muhonen et al., Nature Nanotechnology 9, 986 (2014) [6] A. Laucht, et al., Science Advances 1, 1500022 (2015) [7] J. P. Dehollain, et al., Nature Nanotechnology, DOI: 10.1038/NNANO.2015.262 (2015) [8] S. Freer, et al., in preparation [9] R. Kalra, et al., in preparation [10] A. Laucht, et al., in preparation

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