Single and double hole quantum dots in strained Ge/SiGe quantum wells

Hardy, Will; Harris, Charles Thomas; Su, Yu-Chia; Chuang, Yen; Moussa, Jonathan E.; Maurer, Leon; Li, Jiun-Yun; Lu, Tzu-Ming; Luhman, Dwight

doi:10.1088/1361-6528/ab061e

Cited by 37 publications

(28 citation statements)

References 42 publications

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“…The hole effective mass m * is extracted by fitting the damping of the SdH oscillation amplitude with increasing temperature at B = 1.4 T (Figure g, see the Experimental Section). The obtained value m * = (0.090 ± 0.002) m e , where m e is the free electron mass, is comparable to previous reports in Ge/SiGe at similar densities . The quantum lifetime τ q at 1.7 K is extracted by fitting the SdH oscillation envelope .…”

Section: Resultssupporting

confidence: 82%

“…Indeed, gate controlled quantum dots, ballistic 1D channels, and ballistic phase coherent superconductivity were demonstrated recently by using undoped Ge/SiGe. So far the added complexity in developing reliable gate‐stacks has limited the investigation of quantum transport properties in undoped Ge/SiGe to devices with mobilities significantly inferior compared to modulation‐doped structures …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Sammak

Sabbagh

Hendrickx

et al. 2019

Adv Funct Materials

127

126

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Buried-channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 10 5 cm 2 V −1 s −1 ) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top-gate of a dopant-less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 10 11 cm −2 , light effective mass (0.09m e ), and high effective g-factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies.

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Section: Resultssupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Sammak

Sabbagh

Hendrickx

et al. 2019

Adv Funct Materials

127

126

View full text Add to dashboard Cite

show abstract

“…Holes confined in quantum dots [13,14] have recently attracted much attention due to the possibility of fast singlequbit control by virtue of a strong spin-orbit interaction (SOI) [15][16][17][18][19][20][21] and slow decoherence owing to the suppressed hyperfine interaction [19,[22][23][24][25]. Single-shot readout [26], exchange-coupled quantum dots [27,28], and two-qubit gates [29] have recently been realized in systems where the heavy-hole (HH) and light-hole (LH) states are well separated.…”

Section: Introductionmentioning

confidence: 99%

Exchange interaction of hole-spin qubits in double quantum dots in highly anisotropic semiconductors

Hetényi

Kloeffel

Loss

2020

Phys. Rev. Research

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We study the exchange interaction between two hole-spin qubits in a double quantum dot setup in a silicon nanowire in the presence of magnetic and electric fields. Based on symmetry arguments we show that there exists an effective spin that is conserved even in highly anisotropic semiconductors, provided that the system has a twofold symmetry with respect to the direction of the applied magnetic field. This finding facilitates the definition of qubit basis states and simplifies the form of exchange interaction for two-qubit gates in coupled quantum dots. If the magnetic field is applied along a generic direction, cubic anisotropy terms act as an effective spin-orbit interaction introducing novel exchange couplings even for an inversion symmetric setup. Considering the example of a silicon nanowire double dot, we present the relative strength of these anisotropic exchange interaction terms and calculate the fidelity of the √ SWAP gate. Furthermore, we show that the anisotropyinduced spin-orbit effects can be comparable to that of the direct Rashba spin-orbit interaction for experimentally feasible electric field strengths.

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“…Research on germanium mostly focused on self-assembled nanowires [18][19][20] and demonstrated single-shot spin readout [21] and coherent spin control [15]. However, strained germanium quantum wells were recently shown to support the formation of gate-controlled planar hole quantum dots [22,23]. Now, the crucial challenge is the demonstration of coherent control in this platform and the implementation of qubit-qubit gates for quantum information with holes.Here, we make this step and demonstrate single and two qubit logic with holes in planar germanium.…”

mentioning

confidence: 99%

Fast two-qubit logic with holes in germanium

Hendrickx

Franke

Sammak

et al. 2020

Nature

275

283

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The promise of quantum computation with quantum dots has stimulated widespread research. Still, a platform that can combine excellent control with fast and high-fidelity operation is absent. Here, we show single and two-qubit operations based on holes in germanium. A high degree of control over the tunnel coupling and detuning is obtained by exploiting quantum wells with very low disorder and by working in a virtual gate space. Spin-orbit coupling obviates the need for microscopic elements and enables rapid qubit control with Rabi frequencies exceeding 100 MHz and a singlequbit fidelity of 99.3 %. We demonstrate fast two-qubit CX gates executed within 75 ns and minimize decoherence by operating at the charge symmetry point. Planar germanium thus matured within one year from a material that can host quantum dots to a platform enabling two-qubit logic, positioning itself as a unique material to scale up spin qubits for quantum information.Gate-defined quantum dots were recognized early on as a promising platform for quantum information [1] and a plethora of materials stacks has been investigated as host material. Initial research mainly focused on the low disorder semiconductor gallium arsenide [2,3]. Steady progress in the control and understanding of this system culminated in the initial demonstration and optimization of spin qubit operations [4,5] and the realization of rudimentary analog quantum simulations [6]. However, the omnipresent hyperfine interactions in group III-V materials seriously deteriorate the spin coherence, despite attempts to mitigate this by nuclear polarization [7]. Drastic improvements to the coherence times could be achieved by switching to the group IV semiconductor silicon, in particular when defining spin qubits in isotopically purified host crystal with vanishing concentrations of nonzero nuclear spin [8]. This enabled single qubit rotations with fidelities beyond 99.9% [9] and the execution of two-qubit logic gates with fidelities up to 98% [10-13], underlining the potential of spin qubits for quantum computation. Nevertheless, quantum dots in silicon are often formed at unintended locations and control over the tunnel coupling determining the strength of two-qubit interactions is limited. Moreover, the absence of a sizable spin-orbit coupling for electrons requires the inclusion of microscopic components such as onchip striplines or nanomagnets close to each qubit, which seriously complicates the design of large and dense 2D-structures. This, combined with the limited control over the location and coupling of the dots, remains an outstanding challenge for the scalability of these systems and a platform that can overcome these limitations would be highly desirable. * These two authors contributed equally to this work Hole states in semiconductors typically exhibit strong spinorbit coupling, which has enabled the demonstration of fast single qubit rotations [14,15] and additionally, unlike electrons, holes do not suffer from nearby valley states. In silicon, unfavorable band alignment...

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Single and double hole quantum dots in strained Ge/SiGe quantum wells

Cited by 37 publications

References 42 publications

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Exchange interaction of hole-spin qubits in double quantum dots in highly anisotropic semiconductors

Fast two-qubit logic with holes in germanium

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