Quantinuum extends its significant lead in quantum computing, achieving historic milestones for hardware fidelity and Quantum Volume

By Ilyas Khan, Founder and Chief Product Officer, Jenni Strabley, Sr Director of Offering Management

All quantum error correction schemes depend for their success on physical hardware achieving high enough fidelity. If there are too many errors in the physical qubit operations, the error correcting code has the effect of amplifying rather than diminishing overall error rates. For decades now, it has been hoped that one day a quantum computer would achieve “three 9's” – an iconic, inherent 99.9% 2-qubit physical gate fidelity – at which point many of the error-correcting codes required for universal fault tolerant quantum computing would successfully be able to squeeze errors out of the system.

That day has now arrived. Building on several previous laboratory demonstrations ^{1 2 3}, Quantinuum has become the first company ever to achieve “three 9's” in a commercially-available quantum computer, with the first demonstration of 99.914(3)% 2-qubit gate fidelity, showing repeatable performance across all qubit pairs on our H1-1 system that is constantly available to customers. This production-environment announcement is a marked difference to one-offs recorded in carefully contrived laboratory conditions. This demonstrates what will fast become the expected standard for the entire quantum computing sector.

Quantinuum is also announcing another milestone, a seven-figure Quantum Volume (QV) of 1,048,576 – or in terms preferred by the experts, 2²⁰ – reinforcing our commitment to building, by a significant margin, the highest-performing quantum computers in the world.

These announcements follow a historic month that started when we proved our ability to scale our systems to the sizes needed to solve some of the world’s most pressing problems – and in a way that offers the best path to universal quantum computing.  

On March 5^th, 2024, Quantinuum researchers disclosed details of our experiments that provide a solution to a totemic problem faced by all quantum computing architectures, known as the wiring problem. Supported by a video showing qubits being shuffled through a 2-dimensional grid ion-trap, our team presented concrete proof of the scalability of the quantum charge-coupled device (QCCD) architecture used in our H-Series quantum computers. 

Stop-motion ion transport video showing a chosen sorting operation implemented on an 8-site 2D grid trap with the swap-or-stay primitive. The sort is implemented by discrete choices of swaps or stays between neighboring sites. The numbers shown (indicated by dashed circles) at the beginning and end of the video show the initial and final location of the ions after the sort, e.g. the ion that starts at the top left site ends at the bottom right site. The stop-motion video was collected by segmenting the primitive operation and pausing mid-operation such that Yb fluorescence could be detected with a CMOS camera exposure.

On April 3^rd, 2024 in partnership with Microsoft, our teams announced a breakthrough in quantum error correction that delivered as its crowning achievement the most reliable logical qubits on record.

We revealed detailed demonstrations in an arXiv pre-print paper of the reliability achieved via 4 logical qubits encoded into just 30 physical qubits on our System Model H2 quantum computer. Our joint teams were able to demonstrate logical circuit error rates far below physical circuit error rates, a capability that our full-stack quantum computer is currently the only one in the world with the fidelity required to achieve. 

Explaining the importance of 2-qubit gate fidelity

Reaching this level of physical fidelity is not optional for commercial scale computers – it is essential for error correction to work, and that in turn is a necessary foundation for any useful quantum computer. Our record two-qubit gate fidelity of 99.914(3)% marks a symbolic inflection point for the industry: at ”three 9's” fidelity, we are nearing or surpassing the break-even point (where logical qubits outperform physical qubits) for many quantum error correction protocols, and this will generate great interest among research and industrial teams exploring fault-tolerant methods for tackling real-world problems.

Without hardware fidelity this good, error-corrected calculations are noisier than un-corrected computations. This is why we call it a “threshold” – when gate errors are “above threshold”, quantum computers will remain noisy no matter what you do. Below threshold, you can use quantum error correction to push error rates way, way down, so that quantum computers eventually become as reliable as classical computers.  

Four years ago, Quantinuum claimed that it would improve the performance of its H-Series quantum computers by 10x each year for five years, when measured by the industry’s most widely recognized benchmark, QV (an industry standard not to be confused with less comprehensive metrics such as Algorithmic Qubits). 

Today’s achievement of a 2²⁰ QV – which as with all our demonstrations was achieved on our commercially-available machine – shows that our team is living up to this audacious commitment. We are completely confident we can continue to overcome the technical problems that stand in the way of even better fidelity and QV performance. Our QV data is available on GitHub, as are our hardware specifications

The combination of high QV and gate fidelities puts the Quantinuum system in a class by-itself – it is far and away the best of any commercially-available quantum computer.

‍QCCD: the path to fault tolerance

Additionally, and notably, these benchmarks were achieved “inherently”, without error mitigation, thanks to the H Series’ all-to-all connectivity and QCCD architecture. Full connectivity results in less errors when running large, complicated circuits. While other modalities depend on error mitigation techniques, such techniques are not scalable and present only a modest near-term value. 

Lower physical error and high connectivity means our quantum computers have a provably lower overhead for error-corrected computation.

Looking more deeply, experts look for high fidelities that are valid in all operating zones and between any pair of qubits. In contrast to our competitors, this is precisely what our H Series delivers. We do not suffer from a broad distribution of gate fidelities between different pairs of qubits, meaning that some pairs of qubits have significantly lower fidelities. Quantinuum is the only quantum computing company with all qubit pairs boasting above 99.9% fidelity.

Alongside these benefits and demonstrations of scalability, fidelity, connectivity, and reliability, it is worth noting how these features impact what arguably matters the most to users – time to solution. In the QCCD architecture, speed of operations is decoupled from speed to reach a computational solution thanks to a combination of:

• a better signal to noise ratio than other modalities
• drastically reducing or eliminating the number of swap gates required (because we can move our ions through space), and
• reducing the number of trials required for an accurate result.

The net effect is that for increasingly complex circuits it takes a high-fidelity QCCD-type quantum computer less time to achieve accurate results than other 2D connected or lower-fidelity architectures.

“Getting to three 9’s in the QCCD architecture means that ~1000 entangling operations can be done before an error occurs. Our quantum computers are right at the edge of being able to do computations at the physical level that are beyond the reach of classical computers, which would occur somewhere between 3 nines and 4 nines. Some tasks become hard for classical computers before this regime (e.g. Google’s random circuit sampling problem) but this new regime allows for much less contrived problems to be solved. At that point, these machines become real tools for new discoveries – albeit they will still be limited in what they can probe, likely to be physics simulations or closely related problems,” said Dave Hayes, a Senior R&D manager at Quantinuum.

“Additionally, these fidelities put us, some would say comfortably, within the regime needed to build fault-tolerant machines. These fidelities allow us to start adding more qubits without needing to improve performance further, and to take advantage of quantum error correction to improve the computational power necessary for tackling truly large problems. This scaling problem gets easier with even better fidelities (which is why we’re not satisfied with 3 nines) but it is possible in principle.”

Quantinuum’s new records in fidelity and quantum volume on our commercial H1 device are expected to be achieved on the H2, once upgrades are implemented, underscoring the value that we offer to users for whom stability, reliability and robust performance are pre-requisites. The quantum computing landscape is complex and changing, but we remain at the head of the pack in all key metrics. The relationship with our world-class applications teams means that co-designed devices for solving some of the world’s most intractable problems are a big step closer to reality.

Quantinuum is the world’s leading quantum computing company, and our world-class scientists and engineers are continually driving our technology forward while expanding the possibilities for our users. Their work on applications includes cybersecurity, quantum chemistry, quantum Monte Carlo integration, quantum topological data analysis, condensed matter physics, high energy physics, quantum machine learning, and natural language processing – and we are privileged to support them to bring new solutions to bear on some of the greatest challenges we face.