Alessandro Crippa

Valley blockade and multielectron spin-valley Kondo effect in silicon

We report on the valley blockade and the multielectron Kondo effect generated by an impurity atom in a silicon nano field effect device. According to the spin-valley nature of tunnelling processes, and consistently with those allowed by the valley blockade regime, the manifestation of Kondo effect obeys to the periodicity 4 of the electron filling sequence typical of silicon emerging at occupation N=1, 2, 3. The spin-valley Kondo effect emerges under different kinds of screening depending on the electron filling. By exploiting the valley blockade regime, valley index conservation in the Kondo SU(4) is deduced without the employment of an external magnetic field. Microwave irradiation suppresses the Kondo effect at occupancies up to three electrons.

Electrically driven electron spin resonance mediated by spin–valley–orbit coupling in a silicon quantum dot

The ability to manipulate electron spins with voltage-dependent electric fields is key to the operation of quantum spintronics devices, such as spin-based semiconductor qubits. A natural approach to electrical spin control exploits the spin–orbit coupling (SOC) inherently present in all materials. So far, this approach could not be applied to electrons in silicon, due to their extremely weak SOC. Here we report an experimental realization of electrically driven electron–spin resonance in a silicon-on-insulator (SOI) nanowire quantum dot device. The underlying driving mechanism results from an interplay between SOC and the multi-valley structure of the silicon conduction band, which is enhanced in the investigated nanowire geometry. We present a simple model capturing the essential physics and use tight-binding simulations for a more quantitative analysis. We discuss the relevance of our findings to the development of compact and scalable electron–spin qubits in silicon.Silicon-based qubits: electrically-driven manipulation of spins in double quantum dotsWeak spin–orbit effects in silicon can be exploited to electrically drive electron-spin resonance in a silicon nanowire quantum dot device with low-symmetry confinement potential. Andrea Corna and colleagues at Grenoble’s CEA and University Grenoble Alpes achieved this by fabricating a silicon nanowire device over a silicon-on-insulator wafer, on which the gate accumulation voltages can define two corner quantum dots. Quantum confinement allows the coupling of spin and valley degrees of freedom via spin–orbit coupling, despite its inherent weakness in silicon, when the energy splitting between the valley energy eigenstates matches the magnetic field-induced Zeeman spin splitting. The observation of electric-dipole spin-valley resonance demonstrates the potential of spin–orbit coupling for realizing electric-field-mediated spin control, which will be crucial for large-scale integration of silicon-based spin qubits.

Pauli spin blockade in CMOS double quantum dot devices: Pauli spin blockade in CMOS double quantum dot devices

Silicon quantum dots are attractive candidates for the development of scalable, spin-based qubits. Pauli spin blockade in double quantum dots provides an efficient, temperature independent mechanism for qubit readout. Here we report on transport experiments in double gate nanowire transistors issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low temperature the devices behave as two few-electron quantum dots in series. We observe signatures of Pauli spin blockade with a singlet-triplet splitting ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that transitions which conserve spin are shown to be magnetic-field independent up to B = 6 T.

Modular Printed Circuit Boards for Broadband Characterization of Nanoelectronic Quantum Devices

We report on the development of a modular system of high-frequency printed circuit boards (PCBs) for electrical low-noise characterization of multigate quantum devices. The whole measurement setup comprises PCBs operating from room temperature to a few kelvins, and custom software to control the broadband electronics held at cryogenic and room temperature. The PCBs coupling scheme and the custom tailoring of the user panel make our platform particularly flexible. At the cryogenic stage, one board hosts the electronics for readout. It consists in a custom complementary metal-oxide-semiconductor circuit for the current sensing. It is composed by a multiplexer for a digital selection of the device under test among up to four samples, connected to a cryogenic transimpedance amplifier with two possible gains, the maximum bandwidth of 250 kHz and the minimum equivalent input noise of 10 fA/√Hz. Such board is coupled to the PCB sample holder, where 14 low-frequency input lines bias the devices and control the gates. Four additional high-frequency input paths with a bandwidth of 1 GHz and an isolation lower than -40 dB at 3 GHz have been implemented to apply a few millivolt pulses with a minimum duration of 1 ns. The PCBs assemblage and the cryogenic electronics are electrically characterized at 4.2 K and later used to perform quantum transport spectroscopy and single-charge dynamics readout at a few microsecond scales in two silicon nanoscaled field-effect transistors.