Model of Qubit in Multi-Electron Quantum Dot

Jacak, Lucjan; Krasnyj, J.; Jacak, Dorota; Salejda, W.; Mituś, Antoni C.

doi:10.12693/aphyspola.99.277

Cited by 5 publications

(5 citation statements)

References 28 publications

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“…More recently there has been significant progress in implementing an alternative scheme, 4 in which the singlet and triplet states of two electrons in a DQD make up the qubit. 5,6,7,8,9,10 One particular successful experiment involves initialization, manipulation, and measurement of two-spin singlet and triplet states 4 . Here a (0,2) singlet state is initialized, where (n,m) indicates the occupancy of the left and right dots.…”

Section: Introductionmentioning

confidence: 99%

Realizing singlet-triplet qubits in multivalley Si quantum dots

et al. 2009

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There has been significant progress in the implementation and manipulation of singlet-triplet qubits in GaAs quantum dots. Given the considerably longer spin coherence times measured in Si, considerable interest has been generated recently in Si quantum dots. The physics of these systems is considerably more complex than the physics of GaAs quantum dots owing to the presence of the valley degree of freedom, which constitutes the focus of this work. In this paper we investigate the physics of Si quantum dots and focus on the feasibility of quantum coherent singlet-triplet qubit experiments analogous to those performed in GaAs. This additional degree of freedom greatly increases the complexity of the ground state and gives rise to highly nontrivial and interesting physics in the processes of qubit initialization, coherent manipulation and readout. We discuss the operational definition of a qubit in Si-based quantum dots. We find that in the presence of valley degeneracy a singlet-triplet qubit cannot be constructed, whereas for large valley splitting (>>k_B*T) the experiment is similar to GaAs. We show that experiments on singlet-triplet qubits analogous to those in GaAs would provide a method for estimating the valley coupling in Si. A Zeeman field distinguishes between different initialized states for any valley splitting and provides a tool to determine the size of this splitting

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Section: Introductionmentioning

confidence: 99%

Realizing singlet-triplet qubits in multivalley Si quantum dots

et al. 2009

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“…It rather indicates the enhancement (with increasing magnetic field) of the exchange energy, which is inconvenient for the singlet state and favors the originally excited state -the triplet one. This type of the transition appears at relatively high fields [15] …”

mentioning

confidence: 82%

Quantum information processing on spin degrees of freedom in QDs placed in diluted magnetic semiconductor

Jacak¹,

Krasnyj

Jacak

et al. 2006

Phys. Status Solidi (c)

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The spin degrees of freedom in quantum dot (QD) embedded in a diluted magnetic semiconductor (DMS) medium are considered in a model of a qubit and a gate for quantum information processing (QIP). The qubit is defined as a singlet and triplet pair of states of two electrons in a He-type QD in the DMS medium with strongly enhanced gyromagnetic factor. Methods of qubit rotation (Rabi oscillations) as well as two-qubit operations are suggested and analyzed. Moreover, decoherence related to spin waves (magnon-induced dephasing) in this new system (QD in DMS) is studied, and the relevant time-scale is estimated in accordance with preliminary experimental results.1 Introduction Fault-tolerant quantum computation schemes require the decoherence per quantum gate to be below the threshold of ∼ 10 −6 (DiVincenzo conditions [1]). Feasibility of QIP within the solid state technology employing charge degrees of freedom has been recently intensively investigated [2][3][4]. In spite of still growing accuracy in both QD manufacturing and control techniques, including observation of Rabi oscillations [3,5], demonstration of an all-optically driven gate [3] and entanglement between carriers in interacting dots, the complete implementation of a scalable quantum gate on QDs is still far from being realistic. This is due to extremely inconvenient phonon-induced decoherence in QDs, being the severe obstacle for only-by-light driven gate [6]. Thus spin degrees of freedom in QDs [7][8][9][10] seem to be more promising for QIP, since decoherence of spin is less efficient. However, here the problem is how to accelerate single-qubit operations slowed-down due to a small value of the gyromagnetic factor in semiconductors (the Zeeman splitting in GaAs is ∼ 0.03 meV/T).In practice we usually deal with multi-electron QDs where the spin of a many particle system is sensitive to charge due to Hund-like rules [11]. It is a result of the competition between the direct Coulomb interaction and the exchange interaction of electrons in a magnetic field in the region of single-particle (Fock-Darwin) levels crossing, resulting in the departure from the antiferromagnetic spin alignment to the ferromagnetic filling [11] (according to the first Hund's rule, similarly to ordinary atoms). The characteristic levels crossing with a simultaneous change of the spin polarization is the dominant qualitative picture within the shell description of the dot, robust against many particularities of modelling [11,12], and is convincingly confirmed in experiment [13] in an easily attainable range of magnetic fields of the order of 1 T. Two crossing levels (singlet-triplet transition), well separated from the others, could be considered as a qubit in a multi-electron dot. The energy distance between these levels can be additionally tuned by the magnetic field in wide a region.

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“…1a). This type of the transition appears at sufficiently low fields for dots with a not too large confinement parameter, since the critical field B * [T]∼ ω o [meV]/1.6 [22]. Therefore for a state-of-art vertically stacked pair of self-assembled dots (with ω e o ∼ 30 -50 meV) the value of the critical field lays in an uninteresting region (of the order of 20 -30 T), and for these dots rather the previous type of singlet-triplet transitions for N ≥ 4 are attainable at lower fields.…”

Section: Qubit Definition and Two-qubit Operations In Magnetic Qdsmentioning

confidence: 99%

“…The ground and the first excited state can be approximated by analytical formulae [22]. Our singlet-triplet qubit in a He QD can be thus associated with states denoted by |0 and |1 , where |0 = ψ 00 φ 00 χ 00 ,…”

Section: Qubit Definition and Two-qubit Operations In Magnetic Qdsmentioning

confidence: 99%

Spin-Based Quantum Information Processing in Magnetic Quantum Dots

Jacak

Krasnyj

Jacak

et al. 2005

Open Syst. Inf. Dyn.

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We define the qubit as a pair of singlet and triplet states of two electrons in a He-type quantum dot (QD) placed in a diluted magnetic semiconductor (DMS) medium. The molecular field is here essential as it removes the degeneracy of the triplet state and strongly enhances the Zeeman splitting. Methods of qubit rotation as well as two-qubit operations are suggested. The system of a QD in a DMS is described in a way which allows an analysis of the decoherence due to spin waves in the DMS subsystem.

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Model of Qubit in Multi-Electron Quantum Dot

Cited by 5 publications

References 28 publications

Realizing singlet-triplet qubits in multivalley Si quantum dots

Realizing singlet-triplet qubits in multivalley Si quantum dots

Quantum information processing on spin degrees of freedom in QDs placed in diluted magnetic semiconductor

Spin-Based Quantum Information Processing in Magnetic Quantum Dots

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