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Abstract
Quantum computers are expected to outperform conventional computers in several important applications, from molecular simulation to search algorithms, once they can be scaled up to large numbers—typically millions—of quantum bits (qubits). For most solidstate qubit technologies—for example, those using superconducting circuits or semiconductor spins—scaling poses a considerable challenge because every additional qubit increases the heat generated, whereas the cooling power of dilution refrigerators is severely limited at their operating temperature (less than 100 millikelvin). Here we demonstrate the operation of a scalable silicon quantum processor unit cell comprising two qubits confined to quantum dots at about 1.5 kelvin. We achieve this by isolating the quantum dots from the electron reservoir, and then initializing and reading the qubits solely via tunnelling of electrons between the two quantum dots. We coherently control the qubits using electrically driven spin resonance in isotopically enriched silicon. Si, attaining singlequbit gate fidelities of 98.6 per cent and a coherence time of 2 microseconds during ‘hot’ operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures. Furthermore, we show that the unit cell can be operated at magnetic fields as low as 0.1 tesla, corresponding to a qubit control frequency of 3.5 gigahertz, where the qubit energy is well below the thermal energy. The unit cell constitutes the core building block of a fullscale silicon quantum computer and satisfies layout constraints required by errorcorrection architectures. Our work indicates that a spinbased quantum computer could be operated at increased temperatures in a simple pumped 4He system (which provides cooling power orders of magnitude higher than that of dilution refrigerators), thus potentially enabling the integration of classical control electronics with the qubit array.
Original language  English 

Pages (fromto)  350354 
Number of pages  5 
Journal  Nature 
Volume  580 
Issue number  7803 
DOIs  
Publication status  Published  15 Apr 2020 
MoE publication type  A1 Journal articlerefereed 
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Dive into the research topics of 'Operation of a silicon quantum processor unit cell above one kelvin'. Together they form a unique fingerprint.Projects
 2 Finished

CRYOMET: Fast Cryogenic Microwave Photon Power Metrology in Superconducting Quantum Circuits (CRYOMET)
Tan, K., Sevriuk, V., Zamora Zamora, R., Rasola, M., Santos Teixeira, W. & Gunyho, A.
01/09/2018 → 31/08/2022
Project: Academy of Finland: Other research funding

SPINBUS: Quantum Bus for a Quantum Computer Based on Spins in Silicon
Tan, K.
01/09/2017 → 31/08/2022
Project: Academy of Finland: Other research funding