Spin blockade and exchange in Coulomb-confined silicon double quantum dots

Weber, Bent; Tan, Yui-Hong Matthias; Mahapatra, S.; Watson, Thomas; Ryu, Hoon; Rahman, Rajib; Hollenberg, Lloyd C. L.; Klimeck, Gerhard; Simmons, M. Y.

doi:10.1038/nnano.2014.63

Cited by 140 publications

(145 citation statements)

References 30 publications

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“…3a. These bias triangles can be considered as analogous to transport through a parallel double dot, where for example Pauli spin blockade has recently been observed [23]. Within the lower bias triangle, we observe four linear conductance features in a highresolution current map as seen in Fig.…”

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confidence: 53%

Quantum dot spectroscopy using a single phosphorus donor

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Quantum dot spectroscopy using a single phosphorus donor

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“…The calculations therefore describe the detailed two-electron spectrum of donor qubits over large E-field ranges accounting for both crystal effects and electron-electron exchange and correlation effects. 12 By studying double quantum dots in silicon, 13 we find that an asymmetric 2P-1P system outperforms the symmetric 1P-1P system in exchange controllability with detuning gates. Analogous to exchange tuning in double quantum dots, 14,15 we envision a (1,1) to (2,0) charge transition in both 1P-1P and 2P-1P qubits as a function of a lateral electric field that provides the energy detuning.…”

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confidence: 99%

“…Such an electric field can be applied from either top gates (Figure 1b) in a metal-oxidesemiconductor device or from in-plane gates realised by scanning tunnelling microscope-based lithography (Figure 1c). 13 Placed on either side of the donor qubits, the detuning gates eliminate the need for a sensitive tunnel barrier control by the J-gate. Instead, this design realises a tilt in the potential landscape of the two qubits, as shown in Figure 1d,e, and therefore relaxes the more stringent engineering requirements of donor separations and gate widths of the Kane architecture, leading to a reduced overall gate density in the computer.…”

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Highly tunable exchange in donor qubits in silicon

et al. 2016

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In this article we have investigated the electrical control of the exchange coupling (J) between donor-bound electrons in silicon with a detuning gate bias, crucial for the implementation of the two-qubit gate in a silicon quantum computer. We found that the asymmetric 2P-1P system provides a highly tunable exchange curve with mitigated J-oscillation, in which 5 orders of magnitude change in the exchange coupling can be achieved using a modest range of electric field (3 MV/m) for~15-nm qubit separation. Compared with the barrier gate control of exchange in the Kane qubit, the detuning gate design reduces the gate density by a factor of~2. By combining large-scale atomistic tight-binding method with a full configuration interaction technique, we captured the full two-electron spectrum of gated donors, providing state-of-the-art calculations of exchange energy in 1P-1P and 2P-1P qubits.npj Quantum Information (2016) 2, 16008; doi:10.1038/npjqi.2016.8; published online 12 April 2016 INTRODUCTION Donor qubits in silicon are promising candidates for spin-based quantum computation as they have exceptionally long T 1 (refs 1-3) and T 2 times 4-6 and offer both electron and nuclear spins for encoding quantum information 5-8 utilising commonly used silicon device technology. With recent demonstration of single qubits in silicon with both electronic and nuclear spins of donors, 5,7 the next biggest challenge is to demonstrate two-qubit gates based on the exchange interaction. Ideally, the exchange coupling J in a two-qubit gate needs to be tuned electrically by several orders of magnitude between an 'Off' and an 'On' state within a small and realisable bias range. To achieve this, the popular Kane architecture uses a J-gate between two phosphorus donors to tune the J-coupling. Recently A-gates that tune the hyperfine interaction for individual qubits have been demonstrated. 9 However, in the long run such a J-and A-gate architecture leads to a high gate density, requiring ultra-small gate widths to minimise electrical cross-talk between gates, and precise donor positioning relative to gates. Moreover, the tunability of the exchange coupling is limited both by the electric field range the J-gate can produce and by the field ionisation of the electrons to the surface. Previous calculations have also shown that the J-coupling oscillates as a function of donor separation due to crystal momentum states, 10 and is therefore sensitive to atomic-scale placement errors. All these issues lead to severe constraints in the implementation of a two-qubit gate in donors.In this work, we introduce an alternative design for an exchange gate in a two-qubit donor system, which allows flexibility in device fabrication and in tuning the exchange coupling. In principle, this new design can (1) eliminate the need for additional J-gates between the donors, (2) function with a range of donor separations, (3) provide an~5 orders of magnitude J-tunability within a modest E-field range of~3 MV/m and lowered 'Off' state exchange and (4) mitigate th...

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“…First of all, it appears that the global phase (i.e., φ L ) is not measurable, because there is no physical realizable corresponding to it. We suggest two possible experiments for testing ∆φ directly: i) Measurements of the exchange energy splitting J (references [31] , has been reported [35]. In this work, an asymmetry in the size of the bias triangles in a DQD is attributed to blockade in one bias direction due to the impossibility of inter-valley tunneling.…”

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Valley Phase and Voltage Control of Coherent Manipulation in Si Quantum Dots

2017

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With any roughness at the interface of an indirect-bandgap semiconducting dot, the phase of the valley-orbit coupling can take on a random value. This random value, in double quantum dots, causes a large change in the exchange splitting. We demonstrate a simple analytical method to calculate the phase, and thus the exchange splitting and singlet-triplet qubit frequency, for an arbitrary interface. We then show that, with lateral control of the position of a quantum dot using a gate voltage, the valley-orbit phase can be controlled over a wide range, so that variations in the exchange splitting can be controlled for individual devices. Finally, we suggest experiments to measure the valley phase and the concomitant gate voltage control.The physics of valleys in Si is complicated, both theoretically and experimentally. On the theory side, calculations of the effects of valleys, especially with rough interfaces, often requires very large atomistic simulations; those simulations can sometimes make it more difficult to achieve a simple, intuitive understanding of the underlying physics. In this paper, we present a very simple and intuitively-appealing framework to understand and calculate the effect of the phase of the complex valley-orbit coupling in devices with rough interfaces. On the experimental side, the effects of the valleys can be bound up with spin and orbital effects, thus making effective classical and coherent control of the devices more challenging. We propose a simple experimental method (lateral gate voltages) to both analyze and to control these confounding experimental effects when they arise from the complex phase.Quantum coherent manipulation of electrons in Si has been a very active field of study recently [1][2]. The advantages of Si include low spin-orbit coupling and the ability to isotopically enrich 28 Si, both of which will tend to reduce the decoherence of spin qubits. In addition, the integration with CMOS classical circuitry holds the potential for monolithically integrating qubits with control circuits . The experimental work most relevant for our study is Shi et al [10], which showed experimentally a shift in the single-triplet splitting J for two electrons on a single dot, where J is dominated by the energy difference between single-particle ground and excited valley-orbit states in Si/SiGe. In particular, they measured J as a function of lateral shift using gate voltages; they showed about a 20 % shift, and interpreted it as coming from the change in single-particle valley-orbit energies arising from a rough interface (they solved this for the toy model of a single atomic step).In the vicinity of an interface, the lowest energy valleys are typically perpendicular to the interface, and are split by the valley-orbit coupling, which is defined aswhere|z , |z are the bare valley states centered at k z = ±k 0 = ±(0.85)2π/a 0 , V is the interfacial potential energy, F is the applied electric field, and a 0 is lattice constant; this leads to eigenstates which are symmetric superpositions of...

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Spin blockade and exchange in Coulomb-confined silicon double quantum dots

Cited by 140 publications

References 30 publications

Quantum dot spectroscopy using a single phosphorus donor

Quantum dot spectroscopy using a single phosphorus donor

Highly tunable exchange in donor qubits in silicon

Valley Phase and Voltage Control of Coherent Manipulation in Si Quantum Dots

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