Quebec-based quantum technology company Nord Quantique has detailed its development of bosonic qubit technology with multimode encoding. According to the company, the advancement outlines a path to a major reduction in the number of qubits required for quantum error correction. In doing so, the work enables an approach to quantum computing that will deliver smaller yet more powerful systems that consume a fraction of the energy, the company said. These smaller systems are also simpler to develop to utility-scale due to their size and lower requirements for cryogenics and control electronics. For the demonstration, the company implemented an advanced bosonic code known as Tesseract code, which provides the system with protection against many common types of errors including bit flips, phase flips, and control errors. Another advantage over single-mode encoding is that leakage errors, which remove the qubit from the encoding space, can now be detected. Nord Quantique’s newly developed multimode bosonic qubit. According to the company, the technology, paired with Tesseract code, enables greater quantum error correction capabilities and a path toward smaller and more energy-efficient systems. Courtesy of Nord Quantique. In its demonstration, Nord Quantique used post-selection to filter out imperfect runs, and 12.6% of the data was subsequently discarded each round. This showed excellent stability in the quantum information without measurable decay through 32 error correction cycles. The Tesseract code enables increased error detection, and it is expected that this will translate into additional quantum error correction benefits as more modes are added, according to the company. These results, the company said, are therefore a key milestone in the development of its hardware efficient systems. “The amount of physical qubits dedicated to quantum error correction has always presented a major challenge for our industry," said Julien Camirand Lemyre, CEO of Nord Quantique. "Using physical qubits to create redundancy makes the system large, inefficient and complex, which also increases energy requirements. Multimode encoding allows us to build quantum computers with excellent error correction capabilities, but without the impediment of all those physical qubits. Beyond their smaller and more practical size, our machines will also consume a fraction of the energy, which makes them appealing for instance to [high performance computing] centers where energy costs are top of mind.” The core concept of the multimode approach centers on simultaneously using multiple quantum modes to encode individual qubits. Each mode represents a different resonance frequency inside an aluminum cavity and offers additional redundancy, which protects quantum information. The number of photons populating each mode can also be increased for even more protection, further escalating quantum error correction capabilities. The advancement allows additional error correction capacity and extra means for detecting errors, while keeping the number of qubits static. As these systems scale up, this can lead to what amounts to a 1:1 ratio of physical cavities to logical qubits. In this way, multimode encoding represents a path toward higher performing QEC without increasing the size of the system, according to Nord Quantique. The company believes that the strategy will provide more benefits that compound as they scale, opening avenues for fault-tolerant quantum computing. Examples include a reduction in the effect of auxiliary decay errors, enhancing logical lifetimes through suppression of silent errors, and extraction of confidence information used for further improving errors detection and correction strategies. From an efficiency standpoint, a Nord Quantique quantum computer with 1000+ logical qubits would take up about 20 sq m, compact enough to integrate inside a data center. From an expense standpoint, these systems drive a major reduction of energy consumption. While the amounts fluctuate depending on the computation, using the example of cracking RSA-830 encryption, Nord Quantique projects solving the problem in 1 h at a speed of 1 MHz, consuming 120 kWh. Estimates have those numbers at 1300 kW over 9 days using classical high performance compute, consuming 280,000 kWh, the company said. The estimates also compare favorably against alternate approaches in quantum computing. The team aims to continue improving its results. Nord Quantique's first utility-scale quantum computers with more than a hundred logical qubits are expected by 2029.
