The Microsoft announcement at 2024’s Quantum World Congress this week has created a significant buzz amongst global quantum enthusiasts.
We’ll explore the Microsoft news but let’s take a look at what underlies reliable logical qubits and why they are so important to the industry.
Reliable Logical Qubits
Reliable logical qubits are essential for the development of practical quantum computing, as they form the backbone of error correction protocols, which are critical in maintaining the coherence of quantum states. In contrast to physical qubits, which are prone to errors due to environmental noise and decoherence, logical qubits are encoded using multiple physical qubits to create redundancy. This redundancy allows error correction algorithms to detect and correct errors without disturbing the quantum information stored in the qubit. The development of reliable logical qubits is key to scaling quantum systems beyond small, error-prone experiments.
To create reliable logical qubits, quantum error correction codes such as the surface code and the Bacon-Shor code are commonly employed. The surface code, for instance, arranges qubits on a 2D lattice, where logical qubits are distributed across many physical qubits. This approach can correct both bit-flip and phase-flip errors, two of the most common error types in quantum systems. However, achieving fault tolerance with these codes requires extremely low error rates for physical qubits, often lower than what current quantum hardware can consistently offer. Advances in qubit quality, coherence times, and gate fidelities are therefore crucial for creating logical qubits that can function reliably over long computations.
In addition to error correction, achieving reliable logical qubits involves minimizing overhead in terms of the number of physical qubits needed. Current methods often require hundreds or thousands of physical qubits to encode a single logical qubit, which makes scalability a challenge. As quantum hardware improves and more efficient error-correcting codes are developed, it is hoped that the overhead can be reduced, making quantum computers with reliable logical qubits more feasible. This progress will be key to unlocking the full potential of quantum computing for applications like cryptography, drug discovery, and optimization problems, where error-free operations over long periods are critical.
If you’re looking of a 2-minute video insight into logical qubits, check out Quantinuum’s version here. And for a common language thought experiment, check out my recent substack, The Qubit Thought Experiment, describing the impact of environmental sensitivity.
Microsoft’s Advance
“By expanding Microsoft’s error-correction algorithms and optimizing them for Quantinuum’s H2 machine, which now has 56 qubits with 99.8% two-qubit fidelity, the teams have created 12 highly reliable logical qubits. Previously, Microsoft and Quantinuum entangled two logical qubits in a Bell state preparation, whereas in this study, all 12 logical qubits were entangled in a more complex arrangement known as a cat state, or Greenberger-Horne-Zeilinger (GHZ) state. When these logical qubits were entangled, they exhibited a circuit error rate of 0.0011, which is 22 times better than the corresponding physical qubits’ circuit error rate of 0.024. Microsoft and Quantinuum demonstrated several fault-tolerant computations with the improved logical qubits.”
Who’s Talking?
Global Quantum Intelligence’s Andre König attended the Quantum World Congress presentation and reported that “Jason Zander, EVP Microsoft, took the stage to announce the first ever demonstration of an end-to-end chemistry simulation that combines reliable logical quantum computation with cloud high-performance computing and AI”. GQI’s Quantum Computing Report stated that “This demonstration goes farther than some of the other error correction code experiments we have seen because the team was also able to implement five rounds of logic gates with these circuits. Other experiments have shown error correction to create logical qubits, but not subjecting those logical qubits to gate operations.”
The Quantum Insider reported “One of the next steps for Microsoft is to integrate these fault-tolerant qubits into larger quantum systems. Looking ahead, Microsoft also plans to provide early access to its reliable quantum hardware through the Azure Quantum platform.”
Chemistry Applications
Microsoft recently showcased this first end-to-end chemistry simulation, leveraging its robust logical qubits, cloud-based high-performance computing (HPC), and artificial intelligence (AI). This breakthrough enabled the accurate prediction of the ground-state energy of a chemical catalyst—a task that classical computers struggle with due to the immense computational complexity involved.
Summary
The world of quantum computing is evolving quickly. While not in its’ “prime time”, it is maturing and organizations should be investigating with all due haste. The Microsoft announcement gained significant attention and it won’t be alone as new breakthroughs continue apace.
Brian Lenahan is founder and chair of the Quantum Strategy Institute, author of seven Amazon published books on quantum technologies and artificial intelligence. Brian’s focus on the practical side of technology ensures you will get the guidance and inspiration you need to gain value from quantum now and into the future. Brian does not purport to be an expert in each field or subfield for which he provides science communication.
Brian’s books are available on Amazon. Quantum Strategy for Business course is available on the QURECA platform.
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