A modular creation method to construct a quantum-system-on-chip that incorporates a network of synthetic atom qubits onto a semiconductor chip has been developed by researchers. Credit: Sampson Wilcox and Linsen Li, RLE, edited
An innovative quantum-system-on-chip facilitates the effective manipulation of numerous qubits, pushing the boundaries toward functional quantum computing.
Teams at MIT along with MITRE have unveiled a scalable modular quantum hardware system, accommodating thousands of qubits on a solitary chip, foreseeing improved control and expansibility. By utilizing diamond color centers, this avant-garde design augments extensive quantum communication networks and introduces a novel method, the lock-and-release fabrication technique, to effectively amalgamate these qubits with prevailing semiconductor technologies.
Prospects of Quantum Computing
Picture the ability to swiftly unravel intricate challenges that may take modern supercomputers centuries. This is the vision of quantum computers.
However, to bring this vision to fruition, a system composed of millions of qubit modules needs to be fabricated. The task of creating and handling such an immense quantity of qubits within a hardware framework is daunting, and experts worldwide are attempting to tackle this issue.
Enhancements in Quantum Hardware
In pursuit of this ambition, investigators at MIT and MITRE have introduced a scalable, modular hardware infrastructure that assembles a multitude of interconnected qubits onto a tailored integrated circuit. This design, dubbed the “quantum-system-on-chip” (QSoC), endows the researchers with the precision to regulate and handle a dense array of qubits. Linking multiple microchips through optical networks might lead to a broad quantum communication system.
This QSoC layout makes it feasible for the team to control qubits across 11 distinct frequency bands which proposes a novel “entanglement multiplexing” scheme for quantum informatics of a vast nature.
Revolutionary Manufacturing of Quantum Chips
The assembly of minute arrays of atom-scale qubit chips and their transfer onto a meticulously prepared complementary metal-oxide semiconductor (CMOS) microchip in a singular action is a process years in the making.
“A quantum system’s capability requires multitudes of qubits and exceptional management over them to become effective. We put forth a distinctively new design and a production technique that caters to the scalability demands of a hardware system for a quantum computer,” declares Linsen Li, an electrical engineering and computer science (EECS) graduate scholar and principal contributor to a publication on this framework.
Li’s fellow authors include Ruonan Han, an associate EECS professor, leader of the Terahertz Integrated Electronics Group, and member of the Research Laboratory of Electronics (RLE); Dirk Englund, senior author, EECS professor, primary investigator of the Quantum Photonics and Artificial Intelligence Group and of RLE; as well as collaborators from MIT, Cornell University, the Delft Institute of Technology, the U.S. Army Research Laboratory, and MITRE Corporation. Their paper was recently published in Nature.
Exclusive Characteristics of Diamond Color Centers
The scientists opted for diamond color centers as their qubit medium because of the scalability benefits they offer. Utilizing these qubits previously, they achieved the creation of integrated quantum chips with photonic circuitry.
Diamond color centers, “synthetic atoms” utilized to store quantum data, are solid-state systems which ensures their production is in line with contemporary semiconductor production processes. Their compact size and the extended periods of stability, termed coherence times, are due to the uncontaminated setting supplied by the diamond substance.
Furthermore, diamond color centers are equipped with photonic interfaces that facilitate remote entanglement, or bonding, even with non-adjacent qubits.
“The prevalent notion within the sphere is that the nonuniformity of the diamond color center is a liability when contrasted to identical quantum storage like ions and uncharged atoms. Nonetheless, we convert this obstacle into a benefit by harnessing the unique frequencies of these artificial atoms; each atom functions on its distinct spectral frequency. We can interact with each atom individually by adjusting its voltage into resonance with a laser, akin to setting the frequency on a diminutive radio,” states Englund.
Quantum Communication and Regulation Hurdles
Executing this proves to be exacting as the researchers must apply it on an extensive scale to address the inconsistency in the diamond color center’s qualities within a comprehensive system.
To establish quantum interconnections across qubits, it becomes crucial to synchronize various such “quantum radios” to a common frequency. Scaling to thousands of qubits marks this condition more plausible to achieve. The investigators have overcome this barrier by incorporating a vast set of diamond color center qubits onto a CMOS microchip which furnishes the necessary control mechanisms. The microchip could integrate with in-device digital logic that promptly and autonomously reconfigures.
The voltages facilitate qubits to achieve thorough interconnectivity.
“This adjusts for the system’s uneven characteristics. Utilizing the CMOS framework permits us to swiftly and flexibly modify the qubit frequencies,” Li clarified.
Secure-and-Detach Manufacturing Approach
In order to construct this QSoC, the research team devised a manufacturing technique to position diamond color center “microchiplets” on a CMOS substrate on a grand scale.
They commenced by creating a series of diamond color center microchiplets from a uniform diamond mass. They also crafted and constructed nanoscale optical devices to enhance the gathering efficiency of photons emitted from these color centers in open space.
Next, they structured and charted out the semiconductor chip at the fabrication facility. Employing MIT.nano’s cleanroom, they further processed a CMos chip to include micro-scale connectors that align with the array of diamond microchiplets.
In their laboratory, they established a transfer instrument and utilized a secure-and-detach method to amalgamate the two components by securing the diamond microchiplets within the CMOS chip’s connectors. Since the microchiplets are faintly attached to the diamond substrate, the microchiplets remain in the connectors upon horizontal detachment of the bulk diamond.
“Since we can dictate the creation of both the diamond microchiplets and the CMOS circuit, we can produce a matching pattern. Consequently, we can simultaneously move thousands of diamond chiplets into their respective slots,” says Li.
The scientists showcased a transfer of a 500-micron by 500-micron region for an array containing 1,024 diamond nanoantennas, and they have the potential to escalate the system further by employing larger diamond arrangements and a more sizable CMOS circuit. Interestingly, they discovered that incorporating additional qubits into this setup requires a decreased voltage.
“In essence, the architecture functions more effectively with a greater number of qubits,” asserts Li.
Potential Directions and Evaluation of Performance
Before identifying the optimal microchiplet matrix for the secure-and-detach strategy, the team subjected many nano-configurations to testing. Nevertheless, crafting quantum microchiplets is a complex undertaking, which required several years to refine.
“We’ve refined and perfected the protocol for constructing these diamond nanoconfigurations in the MIT cleanroom. However, it’s a convoluted process; producing these diamond quantum microchiplets necessitated 19 stages of nanofabrication, and the procedures weren’t simple,” he elaborates.
In parallel with their QSoC development, the researchers designed a mechanism for gauging the system’s performance encompassing an extensive scale. They fabricated a specialized cryogenic optical measurement arrangement for this purpose.
Applying this method, they validated an entire circuit comprising over 4,000 qubits, which could be harmonized to a uniform frequency while preserving their quantum spin and photon properties. Additionally, they designed a digital analog simulation bridging the physical experiment with computerized modeling, thereby assisting them in unravelling underlying causative phenomena and planning how to implement the framework more effectively.
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