Jellybeans – a sweet decoration for redundant circuits and computer pages, Engineers show that candy-shaped quantum dots create more breathing space inside a qubit-filled microchip.
The silicon wafers of future quantum computers will be filled with millions, if not billions, of qubits – the basic units of quantum information – to solve the biggest problems facing humanity. And with millions of qubits requiring millions of wires and microchip circuits, it will always be compact.
But now, engineers at UNSW Sydney have taken a big step towards solving the long-standing problem of giving their qubits room to breathe – and it’s for candy.
We’re not the type to rely on sugar rushes to get us through the 3 p.m. slump. But the jellybean quantum dots – elongated regions between pairs of qubits create space for uninterrupted wiring as the qubits connect to each other.
As lead author Associate Professor Arne Laucht explains, the quantum jellybean signal is not a new concept in quantum computing and has been considered as a solution to some of the many paths leading to the construction of the first quantum computer job.
It has been demonstrated in various systems such as gallium arsenide. But this has not been demonstrated in silicon before,” he said.
Silicon is undoubtedly one of the most important materials in quantum computers, A/Prof. Laucht said the infrastructure to create future quantum computer chips already exists, as we use silicon chips in classical computers. Another advantage is that you can install many qubits (in the form of electrons) on a single chip.
“But because the qubits must be close enough to share information with each other, putting a wire between each pair will be a challenge.”
In a study published today in Advanced Materials, the UNSW engineering team explains how they have shown in the laboratory that jellybean quantum dots are possible in silicon. This paves the way for the qubit space to ensure that the necessary wires can be inserted to connect and control the qubits between them.
How it works
In conventional quantum dots using spin qubits, single electrons are drawn from the electron pool in silicon to sit below a ‘quantum threshold’ – where each electron’s spin represents a quantum state. For example, scaling up can represent 0 and scaling down can represent 1. Each qubit can be controlled by an oscillating magnetic field.
But to implement the quantum algorithm, we also need two qubit gates, where the control of one qubit is in the other state. In order for this to work, the two quantum dots must be kept close, a few tens of nanometers apart so that their spins can synchronize with each other. (To put that in perspective, a single human hair is about 100,000 nanometers.)
But separating them to create space for wiring has always been a challenge facing scientists and engineers. The problem is that when the qubits are connected, they stop interacting.
The jellybean solution represents a way to have both: perfectly spaced qubits continuously interact with each other. To make a jellybean, engineers found a way to create chains of electrons by trapping many electrons between qubits. This acts as a kind of quantum cell phone so that the two qubit electrons attached to the end of the jellybean can continue to communicate. Only the electrons at each end are involved in the calculation, while the electrons in the jellybean are there to interact with each other when they leave.
The lead author of the paper, former doctoral student Zeheng Wang, said that the number of electrons added to a jellybean quantum dot is the key to how they organize themselves.
“We showed in the paper that if you put a few electrons into this pool of electrons that you have underneath, they break up into little puddles. So it’s not a jellybean Moving on to the quantum dot, it’s smaller here, and bigger in there. We are talking about a total of three to ten electrons.
“It’s only when you get a large number of electrons, say 15 or 20 electrons, that the jellybean continues to change. And that’s where you have your definition clear and say you can connect qubits to each other.
The post-jellybean quantum world
A/Prof. Laucht pointed out that there is still a lot of work to be done. The team’s efforts for this paper focused on demonstrating that jellybean quantum dots are possible. The next step is to put the active qubits inside or on the edge of the jellybean quantum dot and make them communicate.
“It’s good to see this work done. This builds our confidence that a jellybean couple can be used in a silicon quantum computer, and we’re excited to try adding qubits next.
Source: The University of New South Wales
