Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold.

Practical Quantum computing hinges on the ability to control large numbers of qubits with high fidelity. Quantum dots define a promising platform due to their compatibility with semiconductor manufacturing. Moreover, high-fidelity operations above 99.9% have been realized with individual qubits, though their performance has been limited to 98.67% when driving two qubits simultaneously. Here we present single-qubit randomized benchmarking in a two-dimensional array of spin qubits, finding native gate fidelities as high as 99.992(1)%. Furthermore, we benchmark single qubit gate performance while simultaneously driving two and four qubits, utilizing a novel benchmarking technique called N-copy randomized benchmarking, designed for simple experimental implementation and accurate simultaneous gate fidelity estimation. We find two- and four-copy randomized benchmarking fidelities of 99.905(8)% and 99.34(4)% respectively, and that next-nearest neighbor pairs are highly robust to cross-talk errors. These characterizations of single-qubit gate quality are crucial for scaling up quantum information technology.

Spin Relaxation Benchmarks and Individual Qubit Addressability for Holes in Quantum Dots.

We investigate hole spin relaxation in the single- and multihole regime in a 2 × 2 germanium quantum dot array. We find spin relaxation times T1 as high as 32 and 1.2 ms for quantum dots with single- and five-hole occupations, respectively, setting benchmarks for spin relaxation times for hole quantum dots. Furthermore, we investigate qubit addressability and electric field sensitivity by measuring resonance frequency dependence of each qubit on gate voltages. We can tune the resonance frequency over a large range for both single and multihole qubits, while simultaneously finding that the resonance frequencies are only weakly dependent on neighboring gates. In particular, the five-hole qubit resonance frequency is more than 20 times as sensitive to its corresponding plunger gate. Excellent individual qubit tunability and long spin relaxation times make holes in germanium promising for addressable and high-fidelity spin qubits in dense two-dimensional quantum dot arrays for large-scale quantum information.

A single-hole spin qubit.

Qubits based on quantum dots have excellent prospects for scalable quantum technology due to their compatibility with standard semiconductor manufacturing. While early research focused on the simpler electron system, recent demonstrations using multi-hole quantum dots illustrated the favourable properties holes can offer for fast and scalable quantum control. Here, we establish a single-hole spin qubit in germanium and demonstrate the integration of single-shot readout and quantum control. We deplete a planar germanium double quantum dot to the last hole, confirmed by radio-frequency reflectrometry charge sensing. To demonstrate the integration of single-shot readout and qubit operation, we show Rabi driving on both qubits. We find remarkable electric control over the qubit resonance frequencies, providing great qubit addressability. Finally, we analyse the spin relaxation time, which we find to exceed one millisecond, setting the benchmark for hole quantum dot qubits. The ability to coherently manipulate a single hole spin underpins the quality of strained germanium and defines an excellent starting point for the construction of quantum hardware.

Fast two-qubit logic with holes in germanium.

Universal quantum information processing requires the execution of single-qubit and two-qubit logic. Across all qubit realizations1, spin qubits in quantum dots have great promise to become the central building block for quantum computation2. Excellent quantum dot control can be achieved in gallium arsenide3-5, and high-fidelity qubit rotations and two-qubit logic have been demonstrated in silicon6-9, but universal quantum logic implemented with local control has yet to be demonstrated. Here we make this step by combining all of these desirable aspects using hole quantum dots in germanium. Good control over tunnel coupling and detuning is obtained by exploiting quantum wells with very low disorder, enabling operation at the charge symmetry point for increased qubit performance. Spin-orbit coupling obviates the need for microscopic elements close to each qubit and enables rapid qubit control with driving frequencies exceeding 100 MHz. We demonstrate a fast universal quantum gate set composed of single-qubit gates with a fidelity of 99.3 per cent and a gate time of 20 nanoseconds, and two-qubit logic operations executed within 75 nanoseconds. Planar germanium has thus matured within a year from a material that can host quantum dots to a platform enabling two-qubit logic, positioning itself as an excellent material for use in quantum information applications.

Gate-controlled quantum dots and superconductivity in planar germanium.

Superconductors and semiconductors are crucial platforms in the field of quantum computing. They can be combined to hybrids, bringing together physical properties that enable the discovery of new emergent phenomena and provide novel strategies for quantum control. The involved semiconductor materials, however, suffer from disorder, hyperfine interactions or lack of planar technology. Here we realise an approach that overcomes these issues altogether and integrate gate-defined quantum dots and superconductivity into germanium heterostructures. In our system, heavy holes with mobilities exceeding 500,000 cm2 (Vs)-1 are confined in shallow quantum wells that are directly contacted by annealed aluminium leads. We observe proximity-induced superconductivity in the quantum well and demonstrate electric gate-control of the supercurrent. Germanium therefore has great promise for fast and coherent quantum hardware and, being compatible with standard manufacturing, could become a leading material for quantum information processing.

Strong spin-photon coupling in silicon.

Long coherence times of single spins in silicon quantum dots make these systems highly attractive for quantum computation, but how to scale up spin qubit systems remains an open question. As a first step to address this issue, we demonstrate the strong coupling of a single electron spin and a single microwave photon. The electron spin is trapped in a silicon double quantum dot, and the microwave photon is stored in an on-chip high-impedance superconducting resonator. The electric field component of the cavity photon couples directly to the charge dipole of the electron in the double dot, and indirectly to the electron spin, through a strong local magnetic field gradient from a nearby micromagnet. Our results provide a route to realizing large networks of quantum dot-based spin qubit registers.

Diagnostic efficacy of the Liver Imaging-Reporting and Data System (LI-RADS) with CT imaging in categorising small nodules (10-20 mm) detected in the cirrhotic liver at screening ultrasound.

AIM: To estimate the diagnostic accuracy of the Liver Imaging-Reporting and Data System (LI-RADS) with computed tomography (CT) for diagnosing hepatic nodules (10-20 mm) detected in cirrhotic livers. MATERIALS AND METHODS: Fifty-five patients with liver cirrhosis and a solitary nodule (10-20 mm in diameter) detected via ultrasound surveillance, underwent hepatic CT and fine-needle biopsy. All the CT images were analysed and the lesions were categorised into five categories according to the LI-RADS. RESULTS: Final diagnoses of the 55 nodules were as follows: 34 hepatocellular carcinomas (HCCs), one intrahepatic cholangiocarcinomas, one adrenocortical carcinoma metastasis, and 19 benign lesions. None (0%) of four LI-RADS category 1 lesions, two (22%) of nine category 2 lesions, seven (50%) of 14 category 3 lesions, two (67%) of three category 4 lesions, 22 (96%) of 23 category 5 lesions and one (50%) of two lesions classified as other malignancies was HCC. One category 5 lesion was adrenocortical carcinoma metastasis and one of two lesions categorised as other malignancies was intrahepatic cholangiocarcinoma. In patients with nodules detected at surveillance ultrasound, the best threshold for confident HCC diagnosis was more than LI-RADS category 3. The use of this threshold produced a sensitivity and specificity of 72.7% and 90%, respectively. So combining LI-RADS 4 and 5 categories for confident HCC diagnosis would improve accuracy and sensitivity with no significant impairment of specificity or positive predictive value. CONCLUSION: LIRADS with CT provides a strong validity for the diagnosis of small hepatic nodules, and is very useful to improve the accuracy of CT reports.

Manchester encoder-decoder for optical data communication links.

A new encoder-decoder (CODEC) design of a Manchester coding scheme suitable for optical data communication links is presented. The design is simple and uses off-the-shelf digital electronic components and subsystems. The CODEC can be used for high data rate transmissions, typical of opticalfiber systems and local area networks. The decoder is insensitive to variations in the clock rates within the range of +/-33%, whereas the encoder, which is a simple XOR logic gate, is not affected by clock variations. During high-frequency operation (e.g., at 100 MHz), the CODEC can be operated at a wide range of frequencies (from 66.6 to 133.3 MHz) without modification to the CODEC circuitry. Furthermore, the CODEC can be made to operate at any data rate by a simple change of a single capacitor or a single resistor in the decoder circuit. The CODEC was built in the laboratory by using transistor-transistor logicintegrated circuits. It was experimentally found that with this decoder the transmitted data, as well as the cloc, can be recovered from the Manchester coded signal without being affected by clock variations within the designed range.