Quantum dot hybrid qubits formed from three electrons in double quantum dots represent a promising compromise between high speed and simple fabrication for solid state implementations of single qubit and two qubits quantum logic ports. We derive the Schrieffer-Wolff effective Hamiltonian that describes in a simple and intuitive way the qubit by combining a Hubbard-like model with a projector operator method. As a result, the Hubbard-like Hamiltonian is transformed in an equivalent expression in terms of the exchange coupling interactions between pairs of electrons. The effective Hamiltonian is exploited to derive the dynamical behaviour of the system and its eigenstates on the Bloch sphere to generate qubits operation for quantum logic ports. A realistic implementation in silicon and the coupling of the qubit with a detector are discussed.Comment: 9 pages, 4 figure

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Abstract. We report electronic transport on n-type silicon Single Electron Transistors (SETs) fabricated in Complementary Metal Oxide Semiconductor (CMOS) technology. The n-MOSSETs are built within a pre-industrial Fully Depleted Silicon On Insulator (FDSOI) technology with a silicon thickness down to 10 nm on 200 mm wafers. The nominal channel size of 20×20 nm 2 is obtained by employing electron beam lithography for active and gate levels patterning. The Coulomb blockade stability diagram is precisely resolved at 4.2 K and it exhibits large addition energies of tens of meV. The confinement of the electrons in the quantum dot has been modeled by using a Current Spin Density Functional Theory (CS-DFT) method. CMOS technology enables massive production of SETs for ultimate nanoelectronics and quantum variables based devices.

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A scheme based on Coherent Tunneling by Adiabatic Passage (CTAP) of exchange-only spin qubit quantum states in a linearly arranged double quantum dot chain is demonstrated. Logical states for the qubit are defined by adopting the spin state of three electrons confined in a double quantum dot. The possibility to obtain gate operations entirely with electrical manipulations makes this qubit a valuable architecture in the field of quantum computing for the implementation of quantum algorithms. The effect of the external control parameters as well as the effect of the dephasing on the coherent tunneling in the chain is studied. During adiabatic transport, within a constant energy degenerate eigenspace, the states in the double quantum dots internal to the chain are not populated, while transient populations of the mixed states in the external ones are predicted.A Coherent Tunneling by Adiabatic Passage (CTAP) scheme of exchange-only spin qubit quantum states in a linearly arranged double quantum dot chain is proposed to transfer the information in a quantum circuit by adopting Gaussian pulses.Communication among distant qubits is one of the most challenging requirements towards the implementation of quantum algorithms in solid state system. CTAP in chains of quantum dots where logical states are encoded by one electron has been theoretically predicted in Refs. 1-4 and later experimentally demonstrated in GaAs 5 . The growing interest in quantum computation pushes towards the realization of practical devices that interconnect remote sites composing the quantum circuit to transfer information. Here we extend the formalism of CTAP to the exchange only qubits introduced in Ref. 6 and further developed in Refs. 7-10 . There, logical states are defined by adopting combined spin states of three electrons confined electrostatically in double quantum dots. In particular the logical states are expressed by |0 ≡ |S | ↓ and |1 ≡ 1 3 |T 0 | ↓ − 2 3 |T − | ↑ where |S , |T 0 and |T − are respectively the singlet and triplet states of the spin of a pair of electrons embedded in one dot and | ↑ and | ↓ denote the spin-up and spin-down of the electron in the other dot. The effective Hamiltonian model for a single qubit was derived in Ref. 11 , the corresponding one for the two qubits case was recently developed in Ref. 12 , a universal set of quantum gates is presented in Ref. 13 and an implementation based on Si-MOS quantum dots compatible with the CMOS industrial technological standards is designed in Ref. 14 . The CTAP scheme in our case consists in the tunneling of the three electrons localized initially in the first double quantum dot 6,15 at the head of the chain to the end by using all electrical manipulations. The adiabatic passage takes place when a quantum system prepared in an arbitrary superposition of eigenstates of the Hamiltonian changes slowly during the course of time, that is the transitions between eigenspaces are negligible 4,16 . In particular it is demonstrated that for the chain under study the adiabatic tunneli...

Scalability from single qubit operations to multi-qubit circuits for quantum information processing requires architecture-specific implementations. Semiconductor hybrid qubit architecture is a suitable candidate to realize large scale quantum information processing, as it combines a universal set of logic gates with fast and all-electrical manipulation of qubits. We propose an implementation of hybrid qubits, based on Si Metal-Oxide-Semiconductor (MOS) quantum dots, compatible with the CMOS industrial technologic standards. We discuss the realization of multi-qubit circuits capable of faulttolerant computation and quantum error correction, by evaluating the time and space resources needed for their implementation. As a result, the maximum density of quantum information is extracted from a circuit including 8 logical qubits encoded by the [[7, 1, 3]] Steane code. The corresponding surface density of logical qubits is 2.6 Mqubit/cm 2 .

http://www.gianlucafiori.org/articles/apex.pd

We examine the mobility reduction measured in hafnium-based dielectrics in n-and p-MOSFETs by means of extensive comparison between accurate multi-subband Monte Carlo simulations and experimental data for reasonably mature process technologies. We have considered scattering with remote (soft-optical) phonons and remote Coulomb interaction with single layers and dipole charges. A careful examination of model assumptions and limitations leads us to the conclusion that soft optical phonon scattering cannot quantitatively explain by itself the experimental mobility reduction reported by several groups for neither the electron nor the hole inversion layers. Experimental data can be reproduced only assuming consistently large concentrations of Coulomb scattering centers in the gate stack. However, the corresponding charge or dipole density would result in a large threshold voltage shift not observed in the experiments. We thus conclude that the main mechanisms responsible for the mobility reduction in MOSFETs featuring Hafnium-based high-j dielectric have not been completely identified yet. Additional physical mechanisms that could reconcile simulations with experimental results are suggested and critically discussed.