Development of Quantum Interconnects (QuICs) for Next-Generation Information Technologies

Just as “classical” information technology rests on a foundation built of interconnected information-processing systems, quantum information technology (QIT) must do the same. A critical component of such systems is the “interconnect,” a device or process that allows transfer of information between disparate physical media, for example, semiconductor electronics, individual atoms, light pulses in optical fiber, or microwave fields. While interconnects have been well engineered for decades in the realm of classical information technology, quantum interconnects (QuICs) present special challenges, as they must allow the transfer of fragile quantum states between different physical parts or degrees of freedom of the system. The diversity of QIT platforms (superconducting, atomic, solid-state color center, optical, etc.) that will form a “quantum internet” poses additional challenges. As quantum systems scale to larger size, the quantum interconnect bottleneck is imminent, and is emerging as a grand challenge for QIT. For these reasons, it is the position of the community represented by participants of the NSF workshop on “Quantum Interconnects” that accelerating QuIC research is crucial for sustained development of a national quantum science and technology program. Given the diversity of QIT platforms, materials used, applications, and infrastructure required, a convergent research program including partnership between academia, industry, and national laboratories is required.

Popular Summary

Classical information technologies hinge on the capability of moving information between different locations and often different media. For example, in a modern computer information is stored in magnetic domains in the hard disk, moved to the processor as electric signals in wires, processed in the form of voltages across transistors, and converted to photons to connect to the internet via high-speed optical fiber. Similar to their classical counterparts, quantum information technologies will rely on the ability to move quantum information between different quantum systems that serve distinct tasks. For example, superconducting qubits that are used for quantum computation could be interfaced to a photonic quantum channel that can transmit quantum information to distant processing or memory systems. However, quantum information is extremely fragile, and moving it between systems without destroying it is a daunting but critical task. While many quantum information-processing systems have been recently demonstrated, engineering efficient quantum interconnects (QuICs) between them is a key challenge in achieving practical quantum technologies, such as the quantum internet. Furthermore, interfaces between classical control lines and quantum systems are an important requirement for scaling quantum systems such as quantum computing processors to larger sizes.

In this article, we describe the current state of the art of QuICs and provide a “roadmap” for achieving future goals, as formulated in a recent workshop sponsored by the U.S. National Science Foundation. We identify the key application areas that would be enabled by efficient interconnects and establish performance metrics that will have to be met in order to achieve these new technologies. We highlight the current challenges and opportunities in the development of QuICs – the addressing of which will require a convergent research approach across a broad range of disciplines including engineering, physics, photonics, and material science. This article can serve as a guide for the community and paves the way to achieving QuICs that will enable future quantum technologies.

Figure 1

The broad role of QuICs in quantum information technology. QS, quantum switch; QR, quantum repeater (a device that can relay an entangled state from one set of qubits to a distant set without physically sending an entangled qubit the entire distance); QMod, modular quantum processor; QFC, quantum frequency converter; RNG, random-number generator. The QuICs are indicated by bold red arrows or by wave packets representing photons.