Intel and QuTech address hardware issues between quantum chips in cryogenic environments.
Research findings published in Nature highlight progress towards quantum scalability by controlling silicon qubits with Intel’s Horse Ridge cryogenic chip. A major interconnect bottleneck in current solid-state qubit implementations appears between the quantum chip in a dilution refrigerator and the electronics at room temperature.
Getting the control electronics to operate at high fidelity at cryogenic temperatures is key to overcoming what is called the ‘interconnect or wiring bottleneck’. Intel highlighted how the results published in Nature mark an important milestone in addressing this challenge in quantum connections.
When someone mentions quantum computers, our mind goes to the processors, and the ‘glacial’ temperatures needed to keep the qubits running stably. However, this is only one part of the whole system. There are many factors that determine its ultimate efficiency. Intel is also working on the whole control and manufacturing part in terms of the lithography needed to allow the processor inside a dilution refrigerator to interface with the outside world.
Silicon spin qubits are basically like transistors, devices that Intel is able to produce at a very large scale using lithographic processes. Advanced lithography allows both control electronics and qubits to be fabricated in silicon using a technology that’s compatible with complementary metal-oxide semiconductors (CMOS).
Intel – unlike Google and IBM who use superconducting qubits – is focusing on silicon spin qubits. Silicon spin qubits are basically like transistors and work according to the rotation of the magnetic moment of a single microwave-controlled electron.
When the control electronics system is designed to operate at cryogenic temperatures, it can be integrated with the qubits on the same die, overcoming the above-mentioned ‘wiring bottleneck’.
Intel and QuTech collaboration
Typically, quantum systems use electronics at room temperature, outside the refrigerator, with lots of coaxial cables routed to the processor. According to Intel, this approach is inefficient, as it does not scale with a large number of qubits due to size and thermal load. Cost is also a limiting factor.
Speaking of the work published in Nature, Stefano Pellarano, principal engineer at Intel Labs, said, “Our research is rooted in the idea of quantum practicality, and we’re betting on silicon spin qubits as the optimal path to quantum scalability.” He added, “The results driven in partnership with QuTech, showed promising progress in lifting a major roadblock in quantum scaling.”
Intel and QuTech project is a collaboration between the Delft University of Technology and the Netherlands Organisation for Applied Scientific Research. It addresses hardware issues between quantum chips that are in cryogenic environments and the complex room-temperature electronics that control the qubits.
In the Nature paper, Intel and QuTech highlighted the results of the Horse Ridge controller’s fidelity at cryogenic temperatures while controlling multiple silicon qubits, paving the way for full integration of the controller chip and the qubits on the same die – since they are all fabricated in silicon – or package. Intel and Qutech also demonstrated frequency multiplexing across two qubits using a single wire, simplifying wiring for testing and measurement. Horse Ridge aims to solve this limitation by exploiting multiplexing to reduce the number of radiofrequency cables needed to control the qubits.
In the scientific paper, Intel reports that a cryogenic CMOS control chip operating at 3 kelvins emitted tailored microwave bursts to drive silicon quantum bits cooled to 20 millikelvins. A benchmark of the control chip was performed and demonstrated an electrical performance consistent with qubit operations of 99.99 percent fidelity, assuming ideal qubits. Subsequently, it was repeated to check the real qubits encoded in the spin of single electrons confined in silicon quantum dots. The same fidelity was obtained using the control chip compared to commercial control electronics instruments that operate at room temperature.
In practice, the Horse Ridge chip brings key control functions in the cryogenic cooler at the shortest possible distance from the qubits themselves, reducing the complexity and number of control harnesses. The research, as Intel indicated, shows a commercial CMOS-based cryo-controller achieving consistent control of a two-qubit processor at the same fidelity levels (99.7%) as room-temperature electronics. This is another step in the quantum world that will enable a simplified management of multiple qubits.
This article was originally published on EE Times Europe.
Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.