Silicon Chip Quantum Computing That Has Practical Cooling Costs

Australia developing warmer, cheaper and more robust quantum computing with qubits that need thousands of dollars of refrigeration instead of millions of dollars.

Most current quantum computers need multi-million-dollar refrigeration and as soon as you plug them into conventional electronic circuits they’ll instantly overheat.

Professor Andrew Dzurak and his team at UNSW Sydney have a proof-of-concept silicon chip that works at 1.5 Kelvin. This is 15 times warmer than the main competing chip-based technology being developed by Google, IBM, and others, which uses superconducting qubits.

It needs a few thousand dollars’ worth of refrigeration, rather than the millions of dollars needed to cool chips to 0.1 Kelvin.

Quantum computers can outperform regular computers for certain search and optimization problems.

Nature – Operation of a silicon quantum processor unit cell above one kelvin

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 solid-state 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 28Si, attaining single-qubit gate fidelities of 98.6 percent 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 full-scale silicon quantum computer and satisfies layout constraints required by error-correction architectures. The work indicates that a spin-based 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.

SOURCES- University of New South Wales, Nature
Written By Brian Wang,