Handling errors is one of the hot areas of research to advance quantum computing
Published: 26 Jul 2022 14: 14
A recent article published in Nature has revealed an entirely new phase of matter that has the potential to act as long-term quantum information storage.
Researchers at the Flatiron Institute’s Center for Computational Quantum Physics in New York ran an experiment that subjected a quantum computer’s qubits to “quasi-rhythmic laser pulses” based on the Fibonacci sequence, demonstrating a way of storing quantum information that is less prone to errors. A Fibonacci sequence is a series of numbers where the next value in the sequence is calculated by adding the two preceding numbers (for example, 0, 1, 1, 2, 3, 5).
By shining a laser pulse sequence inspired by the Fibonacci numbers at atoms inside a quantum computer, the physicists created a new phase of matter that has never been observed before. The phase has the benefits of two time dimensions.
The researchers said that information stored in the phase is far more protected against errors than with alternative setups currently used in quantum computers. As a result, the information can exist for much longer without getting garbled – an important milestone for making quantum computing viable, said study lead author Philipp Dumitrescu.
Dumitrescu spearheaded the study’s theoretical component with Andrew Potter of the University of British Columbia in Vancouver, Romain Vasseur of the University of Massachusetts, Amherst, and Ajesh Kumar of the University of Texas in Austin. The experiments were carried out on a quantum computer at Quantinuum in Broomfield, Colorado, by a team led by Brian Neyenhuis.
A typical crystal has a regular, repeating structure, like the hexagons in a honeycomb. A quasicrystal still has order, but its patterns never repeat. Quasicrystals are crystals from higher dimensions projected, or squished down, into lower dimensions. Those higher dimensions can even be beyond physical space’s three dimensions.
For the qubits, Dumitrescu, Vasseur and Potter proposed in 2018 the creation of a quasicrystal in time, rather than space. Whereas a periodic laser pulse would alternate (A, B, A, B, A, B, etc), the researchers created a quasi-periodic laser-pulse regimen based on the Fibonacci sequence. In such a sequence, each part of the sequence is the sum of the two previous parts (A, AB, ABA, ABAAB, ABAABABA, etc). This arrangement is ordered without repeating. It is also a 2D pattern squashed into a single dimension.
The researchers tested the theory using Quantinuum’s quantum computer, pulsing laser light at the computer’s qubits both periodically and using the sequence based on the Fibonacci numbers. The focus was on the qubits at either end of the 10-atom lineup. Dumitrescu said: “With this quasi-periodic sequence, there’s a complicated evolution that cancels out all the errors that live on the edge. Because of that, the edge stays quantum-mechanically coherent much, much longer than you’d expect.”
Toward error-free quantum computing
Meanwhile, in a recent blog post, IBM described its quantum error mitigation strategy as “the continuous path that will take us from today’s quantum hardware to tomorrow’s fault-tolerant quantum computers”.
Over the last few years, said IBM, its researchers have developed and implemented two general-purpose error mitigation methods, called zero noise extrapolation (ZNE) and probabilistic error cancellation (PEC). The ZNE method cancels subsequent orders of the noise affecting the expectation value of a noisy quantum circuit by extrapolating measurement outcomes at different noise strengths.
According to IBM, recent theoretical and experimental advances have shown that PEC can enable noise-free estimators of quantum circuits on noisy quantum computers. IBM has forecast that its approach to error mitigation – which is analogous to how early classical computers developed – will enable it to develop quantum computers with more circuits, which means greater power to solve hard problems.
One such hard problem is predicting the weather, which involves processing complex non-linear differential equations run on classical computer architectures.
The recent hot spell across Europe has shown everyone the importance of accurate weather forecasts. BASF has begun to explore how proprietary quantum algorithms developed by Pasqal could one day be used to predict weather patterns to support its digital farming business. By using parameters generated by weather models, BASF will be able to simulate crop yields and growth stages, as well as predict drift when applying crop protection products.
Advanced weather and climate modelling are usually run on classical computers using physics informed neutral networks (PINN). According to Hyperion Research, 5% of global high-performance computing (HPC) investments are focused on weather modelling.
Rather than rely on HPC, Pasqal aims to solve the underlying complex non-linear differential equations in what it calls “a novel and more efficient” way by implementing so-called quantum neural networks on its neutral atom quantum processors.
John Manobianco, senior weather modeller at BASF’s Agricultural Solutions division, said: “Leveraging Pasqal’s innovation for weather modelling validates quantum computing’s ability to go beyond what can be achieved with classical high-performance computing. Such transformational technology can help us prepare for climate change impacts and drive progress toward a more sustainable future.”
These algorithms will only be viable once researchers and quantum computing companies have improved error handling. However, some of the techniques used to solve problems can be run today on classical computing architectures.
For instance, in a recent podcast, Bloomberg CTO Shawn Edwards discussed why he believes mainstream quantum computing is many years away. Although a lot of progress has been made on the underlying science, Edwards said that some of the more useful things to come out of quantum computing are quantum computing-inspired algorithms. He said the quant teams at Bloomberg have been looking at improving certain algorithms based around quantum computing.
Such quantum-inspired algorithms may be the bridge that enables the mass adoption of quantum computing. Even if error correction is still years away, the research to improve error handling and the development of quantum-inspired code may encourage more IT heads to plan ahead and develop an IT strategy that incorporates quantum computing.