By firing a Fibonacci laser pulse at atoms in a quantum computer, physicists have created an entirely new, strange phase of matter that behaves as if it has two dimensions of time.
The new phase of mattercreated by using lasers to rhythmically shake a strand of 10 ytterbium ions, allows scientists to store information in a much more error-proof manner, opening the path to quantum computers that can hold data for a long time without becoming unreadable. The researchers outlined their findings in a paper published July 20 in the journal Nature (opens in new tab).
Incorporating a theoretical “extra” dimension of time “is a very different way of thinking about phases of matter,” lead author Philipp Dumitrescu, a researcher at the Center for Computational Quantum Physics at the Flatiron Institute in New York City, said. said in a statement. “I’ve been working on this one theory ideas for more than five years, and it’s exciting to see them become reality in experiments.”
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The physicists did not want to create a phase with a theoretical extra time dimension, nor were they looking for a method to allow better storage of quantum data. Instead, they were interested in creating a new phase of matter – a new form in which matter can exist, beyond the standard solid, liquid, gasplasma.
They started building the new stage in the H1 quantum processor from the quantum computer company Quantinuum, which consists of 10 ytterbium ions in a vacuum chamber that are precisely controlled by lasers in a device known as an ion trap.
Ordinary computers use bits, or zeros and ones, to form the basis of all calculations. Quantum computers are designed to use qubits, which can also be in the 0 or 1 state. But that’s about where the similarities end. Thanks to the bizarre laws of the quantum world, qubits can exist in a combination, or superposition, of both the 0 and 1 states until the moment they are measured, after which they randomly collapse into a 0 or a 1.
This strange behavior is key to the power of quantum computing, as it allows qubits to link with each other. quantum entanglementa process that Albert Einstein called “spooky action at a distance.” Entanglement links two or more qubits together, linking their properties so that any change in one particle will cause a change in the other, even if they are large distances from each other. This gives quantum computers the ability to perform multiple calculations simultaneously, increasing their processing power exponentially over classical devices.
But the development of quantum computers has been held back by a major flaw: Qubits don’t just interact and get entangled with each other; because they cannot be perfectly isolated from the environment outside the quantum computer, they also interact with the outside environment, losing their quantum properties and the information they carry, in a process called decoherence.
“Even if you all atoms under strict control, they can lose their ‘quantumness’ by talking to their environment, warming up or interacting with things in ways you hadn’t planned,” Dumitrescu said.
To get around these nasty decoherence effects and create a new, stable phase, the physicists looked at a special set of phases called topological phases. Quantum entanglement enables quantum devices not only to encode information about the single, static positions of qubits, but also to weave them into the dynamic movements and interactions of the entire material – in the form, or topology, of the entangled states of the material. material . This creates a “topological” qubit that encodes information in the form formed by multiple parts rather than one part alone, making the phase much less likely to lose its information.
An important feature of moving from one phase to another is the breaking of physical symmetries – the idea that the laws of physics are the same for an object at any point in time or space. As a liquid, the molecules in water follow the same physical laws at every point in space and in every direction. But if you cool water enough to turn it into ice, the molecules will pick regular points along a crystal structure or lattice to rearrange themselves. Suddenly the water molecules have preferred points in space to occupy, and they leave the other points empty; the spatial symmetry of the water is spontaneously broken.
Creating a new topological phase in a quantum computer also depends on breaking the symmetry, but with this new phase, the symmetry is broken not by space, but by time.
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By giving each ion in the chain a periodic shock with the lasers, the physicists wanted to break the continuous time symmetry of the ions at rest and impose their own time symmetry – with the qubits staying the same over certain time intervals – that would lead to a rhythmic topological phase. about the material.
But the experiment failed. Rather than inducing a topological phase that was immune to decoherence effects, the regular laser pulses amplified the noise from outside the system, destroying it less than 1.5 seconds after it was turned on.
After rethinking the experiment, the researchers realized that to create a more robust topological phase, they would have to knot symmetry in the ion strand more than once to reduce the chances of the system becoming deformed. To do this, they decided to find a pulse pattern that did not repeat itself simply and regularly, but nevertheless showed some sort of higher symmetry in time.
This led them to the Fibonacci Sequence, in which the next number of the sequence is created by adding the previous two. While a simple periodic laser pulse could just alternate between two laser sources (A, B, A, B, A, B, and so on), their new pulse train instead ran by combining the two pulses that came before it (A, AB, ABA , ABAAB, ABABABA, etc.).
This pulsing of Fibonacci created a time symmetry that, like a quasicrystal in space, was ordered without ever repeating. And like a quasicrystal, the Fibonacci pulses also imprint a higher dimensional pattern on a lower dimensional surface. In the case of a spatial quasicrystal such as Penrose tiles, a slice of a five-dimensional grid is projected onto a two-dimensional surface. Looking at the Fibonacci pulse pattern, we see that two theoretical time symmetries are smoothed into a single physical one.
“The system essentially gains a bonus symmetry from a nonexistent extra time dimension,” the researchers wrote in the statement. The system appears as a material existing in a higher dimension with two dimensions of time – even if this is physically impossible in reality.
When the team tested it, the new quasi-periodic Fibonacci pulse created a topographic phase that protected the system from data loss for 5.5 seconds of the test. Indeed, they had created a phase that was immune to decoherence for much longer than others.
“With this quasi-periodic series, there’s a complicated evolution that cancels out all the errors that live at the edge,” Dumitrescu said. “Therefore, the fringe stays quantum mechanically coherent for much, much longer than you might expect.”
Although the physicists have achieved their goal, one hurdle remains to make their phase a useful tool for quantum programmers: integrating it with the computational side of quantum computing so that it can be fed into calculations.
“We have this immediate, tantalizing application, but we need to find a way to hook it into the calculations,” Dumitrescu said. “That’s an open issue we’re working on.”
Originally published on Live Science.