Intel Labs, in collaboration with QuTech ‑ a partnership between TU Delft and TNO (Netherlands Organization for Applied Scientific Research) ‑ outlines key technical features of its new cryogenic quantum control chip "Horse Ridge" in a research paper released at the 2020 International Solid-State Circuits Conference (ISSCC) in San Francisco. The paper unveils key technical capabilities of Horse Ridge that address fundamental challenges in building a quantum system powerful enough to demonstrate quantum practicality: scalability, flexibility and fidelity.

"Today, quantum researchers work with just a small number of qubits, using smaller, custom-designed systems surrounded by complex control and interconnect mechanisms. Intel's Horse Ridge greatly minimizes this complexity. By systematically working to scale to thousands of qubits required for quantum practicality, we're continuing to make steady progress toward making commercially viable quantum computing a reality in our future," said Jim Clarke, director of quantum hardware, Intel Labs.The quantum research community is at mile one of a marathon toward demonstrating quantum practicality. Applying quantum computing to practical problems hinges on the ability to scale to, and control, thousands of qubits at the same time with high levels of fidelity. Horse Ridge greatly simplifies today's complex control electronics required to operate such a quantum system by using a highly integrated system-on-chip (SoC) for faster setup time, improved qubit performance and efficient scaling to larger qubit counts required for quantum computing to solve practical, real-world applications.

Key technical details included in the research paper:

• Scalability: The integrated SoC design, implemented using Intel's 22 nm FFL (FinFET Low Power) CMOS technology, integrates four radio frequency (RF) channels into a single device. Each channel is able to control up to 32 qubits leveraging "frequency multiplexing" - a technique that divides the total bandwidth available into a series of non-overlapping frequency bands, each of which is used to carry a separate signal. Leveraging these four channels, Horse Ridge can potentially control up to 128 qubits with a single device, substantially reducing the number of cables and rack instrumentations previously required.
• Fidelity: Increases in qubit count trigger other issues that challenge the capacity and operation of the quantum system. One such potential impact is a decline in qubit fidelity and performance. In developing Horse Ridge, Intel optimized the multiplexing technology that enables the system to scale and reduce errors from "phase shift" - a phenomenon that can occur when controlling many qubits at different frequencies, resulting in crosstalk among qubits. The various frequencies leveraged with Horse Ridge can be "tuned" with high levels of precision, enabling the quantum system to adapt and automatically correct for phase shift when controlling multiple qubits with the same RF line, improving qubit gate fidelity.
• Flexibility: Horse Ridge can cover a wide frequency range, enabling control of both superconducting qubits (known as transmons) and spin qubits. Transmons typically operate around 6 to 7 GHz, while spin qubits operate around 13 to 20 GHz. Intel is exploring silicon spin qubits, which have the potential to operate at temperatures as high as 1 kelvin. This research paves the way for integrating silicon spin qubit devices and the cryogenic controls of Horse Ridge to create a solution that delivers the qubits and controls in one streamlined package.

Intel and QuTech will be presenting findings from their collaborative research in a paper "A Scalable Cryo-CMOS 2-to-20GHz Digitally Intensive Controller for 4×32 Frequency Multiplexed Spin Qubits/Transmons in 22nm FinFET Technology for Quantum Computers" during Session 19 of ISSCC at 1:30 p.m. PT, Tuesday, Feb 18.