The second generation of controller for quantum computers can fit inside the cryogenic fridge includes the ability to manipulate and read qubit states and control the potential of several gates required to entangle multiple qubits.
“With Horse Ridge II, Intel continues to lead innovation in the field of quantum cryogenic controls, drawing from our deep interdisciplinary expertise bench across the Integrated Circuit design, Labs and Technology Development teams,” said Jim Clarke, director of Quantum Hardware for the Components Research Group at Intel. “We believe that increasing the number of qubits without addressing the resulting wiring complexities is akin to owning a sports car, but constantly being stuck in traffic. Horse Ridge II further streamlines quantum circuit controls, and we expect this progress to deliver increased fidelity and decreased power output, bringing us one step closer toward the development of a ‘traffic-free’ integrated quantum circuit.”
The first chip was designed to address the current approach to today’s early quantum systems, which use room-temperature electronics with many coaxial cables that are routed to the qubit chip inside a the dilution refrigerator. This approach limits the scalability to a large number of qubits due to form factor, cost, power consumption, and thermal load to the fridge.
Intel has worked with TU Delft in the Netherlands on the technology, aiming to get the technology down to the point where the controller can be co-packaged with the qubits. That would dramatically reduce the size of quantum computers. The Dutch team worked on the original 128 qubit Horse Ridge controller which used a 180Kbit SRAM for envelope storage, a digital polar modulator, a 1-GSa/s 10-bit I/Q DAC and a wideband RF front-end. The team is now looking at higher perfomrance RF design and ways to get the temperature down from 3K to under 1.5K.
This design simplified the interconnect and used signal processing techniques to accelerate setup time, improve qubit performance, and enable the engineering team to efficiently scale the quantum system to larger qubit counts.
Horse Ridge II adds the ability to generate radio frequency pulses to manipulate the state of the qubit, known as qubit drive, which is a key area of expertise for the Dutch team. It introduces two additional control features, paving the way for further integration of external electronic controls into the SoC operating inside the cryogenic refrigerator. The Qubit readout reads the current qubit state, allowing on-chip, low-latency qubit state detection without storing large amounts of data, saving memory and power. Multigate pulsing provides the ability to simultaneously control the potential of many qubit gates is fundamental for effective qubit readouts and the entanglement and operation of multiple qubits, paving the path toward a more scalable system.
The addition of a programmable microcontroller operating within the integrated circuit enables Horse Ridge II to deliver higher levels of flexibility and sophisticated controls in how the three control functions are executed. The microcontroller uses digital signal processing techniques to perform additional filtering on pulses, helping to reduce crosstalk between qubits.
Horse Ridge II is implemented using the company’s 22-nm low-power FinFET technology (22FFL) and its functionality has been verified at 4 kelvins, says Intel. Today, a quantum computer operates in the millikelvin range – just a fraction of a degree above absolute zero. But silicon spin qubits – the underpinning of the company’s quantum efforts – have properties that could allow them to operate at temperatures of 1 kelvin or higher, which would significantly reduce the challenges of refrigerating the quantum system and allows the co-packaging says the tream at TU Delft.
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