Quantum states are very subtle and can be easily destroyed. But the perfect solution may lie in imperfect crystals
The quantum computing revolution is coming, and a large number of sensors, communication systems, and powerful computers are very close to being realized.
Functional prototypes of quantum computers, such as Google's Sycamore machine, are already running globally. At the heart of these technologies are "qubits" or "qubits," which are the basic units of quantum computing, similar to how bits are the basic units of classical computing.
Now, researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new method to create tiny glowing dots called color centers; They appear in defects within the crystal by taking a known material and twisting it. In turn, these controllable color centers could be used as new methods for generating qubits.
But the big question is: If quantum computers already exist and use qubits, why do we need a new way to make them? The phenomenon that powers qubits, as well as quantum computers, has proven to be the biggest weakness of this emerging technology.
How qubits take advantage of the quantum world
The increased computing power of quantum computers lies in the fact that qubits operate using shocking, often downright disturbing, phenomena in the quantum world.
For example, while bits can take two values—0 or 1, essentially "on" or "off"—superimposed quantum phenomena, in which multiple states of a system overlap, allow qubits to take multiple contradictory values at the same time.
Thus, a single qubit may be in the "on" and "off" states, just the "on" state, or just the "off" state; As qubits are collectively collected to create quantum networks, these possible states increase. This means that a large number of qubits can exist in a large number of states.
Cryostat from the quantum computer at the Leibniz Computing Center, Germany, July 14, 2022. Quantum computers don't store information in the form of bits, which can only assume two possible states, one or zero. Instead, a quantum computer's qubits can be both, i.e. 1 and 0.
Entanglement is another major quantum phenomenon that enables qubits to pass information to each other in a quantum computer. This is the idea that particles can be linked in ways that cannot be described independently. Changing a particle by performing a measurement instantly changes its entangled partner, no matter how far apart the two particles are, even if they are at opposite ends of the universe. This bothered Albert Einstein so much that he described the entanglement as "ghost operations at a distance."
The application of these quantum elements means that while adding bits to a classical computer can linearly expand its computing power, adding qubits to a quantum computer expands exponentially. Mathematically, this means that if a quantum computer has n qubits, those qubits can exist in a superposition of 2.
The entanglement of qubits and storing information in a superposition state makes quantum computers more powerful than classical computers and leads to systems that can solve problems exponentially. However, there is a problem. A big one. Quantum states like entanglement and superposition are very subtle and can be easily broken. This is a major setback for the reliability of quantum computers.
Noise problems
In the laboratory, entangled and superimposed states in quantum systems are destroyed when measured. The problem is that this "measurement" is just one form of interference, which can come from many sources around the quantum system.
The collapse of the superposition or the loss of entanglement can also be caused by interactions with something as simple as particles, magnetic fields, or temperature fluctuations.
This means that quantum computers must operate under extremely controlled conditions, such as very extremely low temperatures, to protect them from any environmental "noise". Even so, the fragility of these states means that quantum computers cannot yet accurately produce large computational chains.
That's why teams like Berkeley Labs are working on new ways to create qubits, hoping they can develop a system that better prevents "noise."
A colorful twist on qubits
Shaul Aloni, Cong Su, Alex Zettl, and Steven Louie synthesized a device made of hexagonal boron nitride twisted layers
Cong Su, a researcher at Berkeley Lab's involvement in the new qubit work, told Popular Mechanics that qubits can be implemented in many different ways, one way is by utilizing color centers in semiconductors, which are basically emission from defects.
Led by Shaul Aloni, a scientist at Berkeley Lab's Molecular Foundry, the team used solid-state "twisted" crystalline layered materials to create these color centers. Their work was published last summer in the journal Nature Materials.
Su explains: "They used hexagonal boron nitride, which has a honeycomb lattice composed of boron and nitrogen atoms. This structure is very similar to graphene, so hexagonal boron nitride is also called white graphene "In this material, they use radiation from defects — which are either intrinsically embedded or intentionally produced by a bombardment of particles inside hexagonal boron nitride — to create color centers.
Because they are microscopic defects in crystalline materials such as diamonds that emit light of a specific color when struck with alternative energy sources such as lasers or electron beams, color sensors can be combined with devices that control light to connect components in quantum processors.
The color center of hexagonal boron nitride is actually brighter than that of diamond, but before this study, scientists had struggled to use the material — a common additive in paint — because it was difficult to create defects at certain locations.
Traditionally, color centers are created using ion implantation. However, due to the lack of spatial control, which creates color centers at random locations, the researchers are trying to limit the position of these color centers using the interface of hexagonal boron nitride and electron beams.
Another hurdle to this study is that, until now, researchers lacked a reliable way to switch color centers in this synthetic material. The team solved these problems by stacking and rotating hexagonal boron nitride layers like a sandwich, with the top layer of the bread rotating relative to the bottom. This has the effect of activating and enhancing ultraviolet (UV) emission in the center of the color.
The researchers were surprised to see that a simple layer distortion could increase the brightness of the color center by nearly two orders of magnitude.
The team hopes the study is the first step toward color-centric devices that engineers can use to build quantum systems or that could be adapted for use in existing quantum systems. However, more work needs to be done before that to improve the fidelity of the color center to reduce errors in the quantum computing process.
Making quantum devices based on color-centered systems still requires a lot of effort, for example, waveguides to connect different qubits together so that they entangle and communicate with each other.
Researchers want to discover and intentionally create more color centers with better characteristics, and they also hope to find other ways to control them.