Computers rule the world. We use them in our offices, our factories, and in our smartphones. In research and industry, supercomputers help design new medicines or create accurate weather reports, but they can't do everything. Our so-called classical computers are set to meet their 'quantum match' sooner rather than later, leading to advancements in how we design new drugs or how we secure and share our data in the future. The quantum computing age is here and growing. At TU/e, we are playing a leading role in welcoming the age of quantum.
It's a bright, sunny Monday afternoon when I knock on the door of Professor Servaas Kokkelmans ' office in the Qubit building at TU/e.
Kokkelmans is the group leader of the Coherence and Quantum Technology group, CQT group for short. As we sit and discuss some of the intricacies of the Qubit building, we're joined by Rianne Lous and Yuri van der Werf . Lous is also a professor at CQT, while Van der Werf is one and a half years into a postdoctoral role.
All three researchers are working on quantum computers, and from the outset of our interview it's clear that they are passionate about working on the development and realization of quantum computers.
QUANTUM COMPUTER VERSUS CLASSICAL COMPUTER
Whether you're reading this article on your computer at home, on your smartphone while travelling on the train to Eindhoven, or on your laptop while waiting at an airport for a flight, you are using a computing device that stores and processes information using bits.
In these everyday computers - which are also known as classical computers, information is stored as 1s and 0s in so-called bits. The bit is the basic unit of information in computers.
In a quantum computer, the basic unit of quantum information is known as a quantum bit or qubit. Like a classical bit, a qubit stores can store a 1 or 0 - but there's a twist. A qubit can store a 1 and 0 simultaneously. Storing two different numbers (1 and 0) or states is known as superposition.
What does this all mean then when it comes to computing performance?
First, a quantum computer can store multiple numbers at the same time thanks to superposition. For instance, a classical computer bit can only store one number - 1 or 0, but a qubit can store 2 numbers at the same time - 1 and 0. If a quantum computer has 10 qubits, it can store 1,024 numbers at the same time!
Second, in theory, a quantum computer could solve complex problems many times faster than a classical computer. For instance, there have been claims that some quantum computers can solve highly complex mathematical problems thousands of years faster than classical computers!
(The neutral atom quantum computer known as Sapphire, which is located at the Qubit building on the TU/e campus. Photo: Bart van Overbeeke)
So, what is a quantum computer?
Four floors below Kokkelmans' 2nd floor office in the Qubit building lies that realization - a collection of prototype quantum computers with the potential to perform calculations that seemed unimaginable to his postdoc self.
With a feel for their enthusiasm, I ask the three to define a quantum computer with the promise that the best answer will be included in the article.
Lous steps up first. "A quantum computer is made out of quantum bits or qubits for short. A qubit can store a value 0 and 1 at the same time. This gives you a superposition - it can hold multiple values at the same time. When one qubit 'talks' to another, they become entangled with each other. More qubits equals more calculating power. The combination of entanglement and superposition is the foundation of the quantum computer."
Kokkelmans' answer echoes part of Lous' answer. "A quantum computer is a device with a computing power that scales exponentially with the number of qubits."
The combination of entanglement and superposition is the foundation of the quantum computer.
Rianne Lous
Finally, Van der Werf contributes her answer. "Like a classical computer, a quantum computer has information carriers, the qubits. But unlike a classical computer where the information carriers store 0 or 1, qubits can store any number between 0 and 1."
Three seemingly different answers then from three quantum physicists. However, borrowing a term from quantum physics, the answers from the three are entangled with each other. Their answers overlap and highlight the novelty and power of quantum computers.
Why quantum computers are so exciting
But why should people be excited to learn more about quantum computers?
Van der Werf answers first. "I was drawn to the world of quantum as it's so fascinating. We're literally grabbing individual atoms one by one in our basement lab in a vacuum and at a temperature that is a million times colder than the temperature of interstellar space (the space between stars in space, ed.). I'm enthralled by where quantum computers could be used in society - from new drug discovery to better online security. It's an exciting time to work in quantum."
Lous shares Van der Werf's enthusiasm. "These are technologies that offer new ways to solve complex problems," says Lous. "We're using atoms as the building blocks of quantum technologies, like quantum computers, and then change these atoms with incredible accuracy."
Now though it's not elusive, it's not a dream - it's reality!
Servaas Kokkelmans
As Van der Werf and Lous share their excitement for quantum computers, Kokkelmans nods in appreciation. Yet his beginnings in the world of quantum computers were very different.
"When I was a postdoc researcher - just like Yuri is now - working on quantum computers, it was an elusive theoretical concept," Kokkelmans says while gesturing towards Van der Werf. "Now though it's not elusive, it's not a dream - it's reality!"
A neutral atom start
The Qubit building is home to quantum computers and a quantum simulator. For the interview, though, we're concentrating on two quantum computers with the gemstone inspired names Ruby and Sapphire. So, what are the building blocks of Ruby and Sapphire? What are their qubits made of?
"Atoms," Kokkelmans answers with a wry smile. "To be more specific, neutral atoms."
Van der Werf weighs in with more details. "Everyone who thinks about a computer thinks about a chip. But this is fundamentally different from what we do - we're working with single atoms."
Neutral atoms are atoms without charge in that they have the same number of protons (which have a positive charge) and electrons (which have a negative charge). Ruby uses rubidium (Rb) atoms, while Sapphire relies on strontium (Sr) atoms.
Everyone who thinks about a computer thinks about a chip. This is different from what we do - we're working with single atoms.
Yuri van der Werf
"If you pick two of either atom and compare them, you'll discover that they are identical in every possible way, which is perfect when you want to build a quantum computer consisting of identical qubits," notes Kokkelmans. "This means that know exactly how each qubit will respond to light, for example, and we don't need to treat each qubit in a special way. They are all the same - so we can treat them all exactly the same."
Van der Werf is working mainly with Ruby, which consists of about 50 qubits, and she points a little more about what makes them identical.
"In its ground state, the electrons in orbit around the nucleus of an atom are in their lowest energy state. If the atoms are all in their ground state then they all look exactly the same. Rubidium has one electron on the outside, which makes it very suitable for defining two possible final states - where it's in a low energy state (0) or a high energy state (1)."
Coldest place in Eindhoven
While neutral atoms like strontium and rubidium are suitable for use as qubits, a special environment is needed for the qubits to function.
"For the atoms to be viable qubits, the environment needs to be controlled. It needs to be cold," says Lous. "And this requires a suite of technologies working together to keep the atoms at a fixed location. But the real enemy here is the heat or thermal energy that atoms can have."
Bumping atoms
Molecules and atoms are zooming around you and bumping into you right now. These have kinetic or moving energy, which is linked to heat. The faster something moves, the hotter it is.
In the neutral atom quantum computers at Qubit, the strontium and rubidium atoms need to be as close to stationary as possible. To achieve this, the atoms need to be kept as cold as possible.
Yet, slowing down the atoms doesn't involve an ultracold fridge, a cryostat, or even liquid helium (which is a liquid at -269 °C). The solution is quainter than that.
"We hold the atom in place with a laser in an artificial ultra-high vacuum," says Van der Werf. "To create the vacuum, we pump the air out of a chamber. If there are no molecules in the chamber, then heat cannot move across the system via convection. Then we fire a high-intensity laser beam with a strong focus at the atom, and the atom then sits in the focus of the laser. This is known as an optical tweezer."
THE KEY PARTS OF A NEUTRAL ATOM QUANTUM COMPUTER
What are the key components of a neutral atom quantum computer besides the need for atoms like strontium or rubidium? Here's the details on three must-haves for such a quantum computer.
An optical tweezers
This is a tweezer made up of light, usually from a laser. It's used to hold cooled-down atoms in place in the quantum computer.
Using an optical tweezer is also quite difficult too. Hitting an atom with a laser can be like trying to find a needle in a haystack.
An ultra-high vacuum
To make it easier to hold the atoms with the optical tweezer, the atoms must be moving slowly or almost stationary. Fast moving atoms are hot, which means that the atoms need to be cooled.
A cooling system - such as cryostat - is not used to cool down the atoms in the quantum computer. Instead an ultra-high vacuum in a chamber is created to constrain the atoms. As the vacuum chamber contains little or no molecules, heat cannot move across the system.
At Qubit, the temperature of the atoms goes down to 4 microkelvin, or 4 millionths of a kelvin. This low temperature is possible because the cooling approach is not used to cool down large setups or electronics. It's just used to cool the atoms in the quantum computer.
Read-write lasers
To read and write data to the qubits, lasers are used. An atom is illuminated by a laser. Depending on its state, the atom will emit light back. For example, if light is emitted this represents one, while the absence of light represents zero.
Lasers are also used to write information to the atoms, which involves adding energy to the atoms, and leads to the electrons around the atoms gaining energy.
(Image on right: Close up shot of the neutral atom quantum computer Sapphire. Photo: Bart van Overbeeke)
Energy consumption
Running lasers and ultra-high vacuum technologies to hold atoms in place sounds like it could require a lot of energy, but that's not the case. "The total electricity consumption for our lab in 2024 was 6 kWh per day, which is about the same as a residential home," notes Lous.
We have the right to call this place the coldest place in Eindhoven as we reach temperatures of about 4 microkelvin, which is super-close to absolute zero.
Servaas Kokkelmans
Kokkelmans is very proud of one incredible fact about the cooling systems they use which involve no fridges, cryostats, or ultra-cold liquids. "We have the right to call this place the coldest place in Eindhoven as we reach temperatures of about 4 microkelvin, which is super-close to absolute zero (-273.15 °C)."
It's not just a numbers game
Located deep in the Qubit basement, the lab which Ruby and Sapphire call home is compact, it's dark when the lights go out, and perhaps the hardest place on campus to get a reliable mobile reception.
The computers stand side-by-side surrounded by control stations, metal shelving, and specialised technologies that help regulate and control the lasers.
When you look at the qubit count though, Ruby and Sapphire's 50 qubits puts it behind several others working on neutral atom quantum computers. US-based Atom computing boasts a system with over 1,200 qubits , while French startup Pasqal (which emerged from research by Nobel Prize winner Alain Aspect) has created a quantum computer with over 1,000 qubits .
Leading the way are researchers at Endres lab at Caltech who have demonstrated the trapping of 6,100 neutral atoms.
Nevertheless, in the neutral atom quantum computer world, the number of qubits isn't the most important aspect as Kokkelmans outlines.
"The media might focus on the number, but in the quantum computing world, that's not the most important thing," says Kokkelmans. "It's more important to have qubits that can be entangled with each other and it must be easy to manipulate individual qubits. This will make the qubits more effective in terms of computing performance."
"We rarely use the word 'quantum'."
Quantum technologies - like quantum computers - emerging from quantum physics might seem fascinating and scary to some. "I think it's about there being a balance. It's going to be new for a lot of people, including scientists in other fields," says Kokkelmans.
When I ask my kids about their thoughts on my work, they say 'Oh Daddy, in your work you just take a word and put quantum in front of it!'
Servaas Kokkelmans
Funnily enough, it's Kokkelmans who gets some interesting reactions from his kids at home. "When I ask my kids about their thoughts on my work, they say 'Oh Daddy, in your work you just take a word and put quantum in front of it!'"
Sitting with the trio of quantum physicists to discuss quantum computers and quantum physics led to a 'quantum conversation' of more than 1 hour 20 minutes. The word 'quantum' featured more than 200 times (According to the transcript for the interview in any case). Such a frequent use of the word 'quantum' isn't normal for quantum physicists.
"When a group of quantum physicists are in a meeting it's rare that you'll hear someone say the word 'quantum'," Lous points out. "We rarely use the word 'quantum'."
"We tend to talk about the properties of atoms, energy levels and other aspects related to exciting atoms (where certain electrons around atoms gain energy and move to higher energy levels which are further away from the center of the atom)," Van der Werf adds. "Quantum is used mainly in outreach activities or when speaking to researchers who are not working in quantum physics."
Shrink down in the future
At Qubit, the future is very bright when it comes to quantum computers.
Over the coming months though, it's going to get brighter when Eindhoven's hybrid quantum computer goes online as part of the Quantum Inspire platform .
We could shrink our computers down in size and really benefit from their computational power.
Rianne Lous
"The hybrid quantum computer combines a classical supercomputer and a quantum computer to solve complex problems," says Kokkelmans. "And the device will be open for anyone to run their quantum programs. We're very excited to be part of the Quantum Inspire platform."
That's the immediate future, but Lous is hoping to see a photonics-inspired revolution in quantum computer design for atoms in the future. "Quantum meets photonics meets electronics is my dream. Now, we use one laser to address many qubits in our setup. Imagine a future chip for quantum computers that contains a dedicated laser for each qubit. We could shrink our computers down in size and really benefit from their computational power."
Who wants a quantum job?
Finally, Van der Werf reflects on the future of quantum jobs where there are many possibilities.
And things are moving fast. All three of us know people right now who are working in the quantum industry in roles that didn't exist five years ago.
Yuri van der Werf
"To work in the quantum industry, you won't need to be a quantum physicist. We need people to build the electronics, to design the lasers, to develop the vacuum technologies, to invent more programming languages. All these people don't necessarily need to be quantum physicists. And things are moving fast. All three of us know people right now who are working in the quantum industry in roles that didn't exist five years ago."
As I leave the office after the interview, I'm filled with the confidence that our Qubit researchers are well placed to have a massive impact on the world of neutral atom quantum computers, and quantum in general.
The coldest place in Eindhoven could very well be home to the hottest advancements in quantum for the region, which could impact the country and the world.
