Abstract
We report on the spin-lattice interaction and coherent manipulation of electron spins in Mn-doped colloidal PbS quantum dots (QDs) by electron spin resonance. We show that the phase memory time,$\phantom{\rule{0.28em}{0ex}}{T}_{M}$, is limited by Mn--Mn dipolar interactions, hyperfine interactions of the protons ($^{1}\mathrm{H}$) on the QD capping ligands with Mn ions in their proximity (1 nm), and surface phonons originating from thermal fluctuations of the capping ligands. In the low Mn concentration limit and at low temperature, we achieve a long phase memory time constant $\phantom{\rule{0.28em}{0ex}}{T}_{M}\ensuremath{\sim}0.9\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$, thus enabling the observation of Rabi oscillations. Our findings suggest routes to the rational design of magnetic colloidal QDs with phase memory times exceeding the current limits of relevance for the implementation of QDs as qubits in quantum information processing.
Highlights
In the last two decades the coherent manipulation of electron spins in semiconductor quantum dots (QDs) has attracted continuously increasing interest for quantum information processing (QIP) applications [1,2]
We show that the phase memory time, TM, is limited by Mn–Mn dipolar interactions, hyperfine interactions of the protons (1H) on the QD capping ligands with Mn ions in their proximity (
A dominant contribution of 1H nuclear spins to electron spin dephasing in comparison to other nuclear spins in the QD is ascribed to the larger gyromagnetic ratio (γ1H/γ207Pb ∼ 5 and γ1H/γ33S ∼ 13) and natural abundance (ß100% for 1H, ß22% for 207Pb, and ß0.8% for 33S) of 1H
Summary
In the last two decades the coherent manipulation of electron spins in semiconductor quantum dots (QDs) has attracted continuously increasing interest for quantum information processing (QIP) applications [1,2]. Spin manipulation has been reported for electron spins confined in lateral [4] and magnetic self-assembled [5] QDs, it still remains largely unexplored in colloidal QDs [6,7]. Colloidal magnetic semiconductor QDs represent an excellent benchmark to study the dephasing effects of electric (phonons) and magnetic (nuclei and unpaired electrons) field fluctuations on electron spin coherence and to explore promising routes to quantum technologies
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