Electrically driven nuclear spin resonance in single-molecule magnets

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Science  06 Jun 2014:
Vol. 344, Issue 6188, pp. 1135-1138
DOI: 10.1126/science.1249802

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  1. Fig. 1 Nuclear spin qubit transistor and its detection scheme.

    (A) Artist’s view of a nuclear spin qubit transistor based on a single TbPc2 molecular magnet. The molecule, consisting of a Tb3+ ion (pink) sandwiched between two Pc-ligands (white), is coupled to source, drain, and gate (not shown) electrodes. The four anisotropic nuclear spin states of the Tb3+ (colored circles) can be manipulated with an electric field pulse. (B) Three coupled subsystems of the transistor: (i) The four-level nuclear spin qubit is hyperfine (HF) coupled to (ii) an Ising-like electronic spin, which in turn is antiferromagnetically exchange (Ex) coupled to (iii) a readout quantum dot.

  2. Fig. 2 Zeeman diagram and nuclear spin detection procedure.

    (A) Zeeman diagram of the TbPc2 molecular magnet, showing the hyperfine split electronic spin ground state doublet Embedded Image and Embedded Image as a function of the external magnetic field Embedded Image parallel to the easy-axis of magnetization. The ligand-field–induced avoided level crossings (colored rectangles) allow for tunneling of the electron spin. (B) The jumps of the conductance g of the readout quantum dot during magnetic-field sweeps are nuclear spin dependent. (C) Histograms of the positions of about 75,000 conductance jumps, showing four nonoverlapping Gaussian-like distributions; each conductance jump can be assigned to a nuclear spin state.

  3. Fig. 3 Rabi oscillations of a single nuclear spin qubit.

    (A) Time-dependent external magnetic field Embedded Image and pulse sequence. The nuclear spin is first initialized in the lower Embedded Image state (init sequence). A subsequent MW pulse of frequency Embedded Image and duration τ induces an effective oscillating magnetic field resulting in coherent manipulation of the two lower states of the nuclear spin qubit. Finally, Embedded Image is swept back to probe the final state of the nuclear spin qubit. (B and C) Rabi oscillations between Embedded Image and Embedded Image states obtained by repeating the above sequence 100 times at each τ, for two different MW powers, (B) PMW = 1 mW and (C) PMW = 1.58 mW.

  4. Fig. 4 Stark shift of the hyperfine coupling and Ramsey fringes.

    (A) Rabi oscillations visibility measured at different MW frequencies for three different gate voltages Embedded Image. (B) Rabi frequencies Embedded Image corresponding to the visibility of (A). The continuous lines are fit to the experimental points following the theoretical expression of the Rabi frequency dependence (see text). (Inset) The relative change Embedded Image with respect to the applied Embedded Image. (C) Time-dependent external magnetic field Embedded Image and pulse sequence. Initialization and probe of the nuclear spin qubit are performed by using the identical protocol as in Fig. 3A. The MW sequence consists of two π/2 pulses, with an increasing interpulse delay τ. (D) Ramsey interference fringes obtained by repeating the procedure of (C) 100 times. Embedded Image = 2.205 V, corresponding to a Rabi frequency Embedded Image = 1.136 MHz and a resonant frequency Embedded Image = 2.449 MHz of the nuclear spin qubit. The measured coherence time Embedded Images.