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Register a new userDynamically controlled charge sensing of a few-electron silicon quantum dot
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We report charge sensing measurements of a silicon metal-oxide-semiconductor quantum dot using a single-electron transistor as a charge sensor with dynamic feedback control. Using digitallycontrolled feedback, the sensor exhibits sensitive and robust detection of the charge state of the quantum dot, even in the presence of charge drifts and random charge rearrangements. The sensor enables the occupancy of the quantum dot to be probed down to the single electron level.
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The advanced nanoscale integration available in silicon complementary metal-oxide-semiconductor (CMOS) technology provides a key motivation for its use in spin-based quantum computing applications. Initial demonstrations of quantum dot formation and spin blockade in CMOS foundry-compatible devices are encouraging, but results are yet to match the control of individual electrons demonstrated in university-fabricated multi-gate designs. We show here that the charge state of quantum dots formed in a CMOS nanowire device can be sensed by using floating gates to electrostatically couple it to a remote single electron transistor (SET) formed in an adjacent nanowire. By biasing the nanowire and gates of the remote SET with respect to the nanowire hosting the quantum dots, we controllably form ancillary quantum dots under the floating gates, thus enabling the demonstration of independent control over charge transitions in a quadruple (2x2) quantum dot array. This device overcomes the limitations associated with measurements based on tunnelling transport through the dots and permits the sensing of all charge transitions, down to the last electron in each dot. We use effective mass theory to investigate the necessary optimization of the device parameters in order to achieve the tunnel rates required for spin-based quantum computation.
Understanding interactions between orbital and valley quantum states in silicon nanodevices is crucial in assessing the prospects of spin-based qubits. We study the energy spectra of a few-electron silicon metal-oxide-semiconductor quantum dot using dynamic charge sensing and pulsed-voltage spectroscopy. The occupancy of the quantum dot is probed down to the single-electron level using a nearby single-electron transistor as a charge sensor. The energy of the first orbital excited state is found to decrease rapidly as the electron occupancy increases from N=1 to 4. By monitoring the sequential spin filling of the dot we extract a valley splitting of ~230 {mu}eV, irrespective of electron number. This indicates that favorable conditions for qubit operation are in place in the few-electron regime.
Transport measurements at cryogenic temperatures through a few electron top gated quantum dot fabricated in a silicon/silicon-germanium heterostructure are reported. Variations in gate voltage induce a transition from an isolated dot toward a dot strongly coupled to the leads. In addition to Coulomb blockade, when the dot is strongly coupled to the leads, we observe the appearance of a zero bias conductance peak due to the Kondo effect. The Kondo peak splits in a magnetic field, and the splitting scales linearly with the applied field. We also observe a transition from pure Coulomb blockade to peaks with a Fano lineshape.
We present a thermometry scheme to extract the temperature of a 2DEG by monitoring the charge occupation of a weakly tunnel-coupled thermometer quantum dot using a quantum point contact detector. Electronic temperatures between 97 mK and 307 mK are measured by this method with an accuracy of up to 3 mK, and agree with those obtained by measuring transport through a quantum dot. The thermometer does not pass a current through the 2DEG, and can be incorporated as an add-on to measure the temperature simultaneously with another operating device. Further, the tuning is independent of temperature.
In this paper we report on a tuneable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by novel charge transfer behaviour.
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