There’s still a long road ahead to scale quantum computers to the million-qubit range and get to the point where they can do anything “really useful” for society.

Current quantum computers are made up of less than 150 qubits and most of this hardware is dominated by a handful of large companies who are following a similar technical route, using superconducting qubits.

**Wafer with quantum computing microchips**

A recent report from McKinsey highlights: “Due to the complexity of the technology, the hardware segment has high risk and long development times. As a result, players require significant capital and highly specialized knowledge. The hardware segment today is dominated by technology giants, most of which entered the market a decade ago and focus on superconducting qubits.”

But start-ups focused on other qubit technologies are now scaling up, according to McKinsey, with many ready to take on the million-qubit challenge in new and innovative ways. Of course, there are many proposed routes to get there, and no one knows exactly who will win the race to millions of qubits — and when.

Nonetheless, we need to be bold and develop technologies that can get us to millions of high-quality qubits so that we can unlock the true potential of quantum computing and solve meaningful problems. By meaningful, that means solving problems that transform people’s lives.

That’s been our focus at Universal Quantum from day one, to change the world for the better with a million-qubit machine and we are busy turning our original blueprint for a large-scale microwave trapped-ion quantum computer into reality.

**Why millions of qubits?**

By their very nature, qubits are error-prone and difficult to control. As a result, quantum computers are unstable, complex systems and addressing these errors is key.

Fortunately, something called quantum error correction exists, which is a collection of algorithms and techniques to identify and fix errors in quantum computers. But for such algorithms to work, the information stored in a single qubit is distributed across other supporting qubits.

Depending on the nature of the hardware you use and the type of algorithm you choose to run, you may need hundreds or thousands of physical qubits to support a single logical qubit.

But one logical qubit is not enough to complete complex calculations to do something useful for society. At the very least, you need hundreds or thousands of logical qubits, each one supported by hundreds or thousands of physical qubits. This is where the requirement for millions of qubits comes from.

Error correction is a problem that needs addressing at the software, hardware and end-user level — something which Innovate UK’s Industrial Strategy Challenge Fund recognized when it recently awarded us a £7.5m consortium grant to build a scalable quantum computer that can correct its own errors and apply this technology to high-impact problems in the aerospace industry.

While the million-qubit range is outside of the scope of this three-year project, it’s a step in the right direction towards scalable quantum computing and achieving something “useful” for society.

So, now we understand why we need millions of qubits, how are we going to get there? Let’s explore the different hardware factors to take into account, focusing on Universal Quantum’s unique design.

**Keeping cool**

To maintain the fragile quantum states of qubits, quantum computers need to operate at low temperatures. This exact temperature is dependent on the type of qubit used.

Superconducting machines require cooling to near absolute zero (which is minus 273 degrees Celsius). As we scale, the refrigeration requirements become increasingly challenging as these machines grow in scale and complexity.

But trapped ion systems do not require such stringent refrigeration requirements, which is important as we scale up the number of qubits. Our trapped-ion technology only requires cooling to 70K, for example.

**Freeing trapped ions**

Qubit connectivity is another important consideration. Superconducting qubits tend to only interact with their nearest neighbors. But trapped-ion qubits are free to move around, making it easier to run complex calculations as these qubits can essentially ‘talk’ to each other as prescribed by a quantum algorithm.

In fact, trapped ion designs have led to many significant world records in the quantum computing sector. But there are still challenges for trapped ion systems as we continue to scale, challenges that our design addresses.

Lose the lasers

In some trapped-ion systems, each qubit requires a laser beam to control its fragile state. Once we scale to millions of qubits, millions of lasers are required for the quantum computer to work, each one perfectly aligned within the fraction of the width of a human hair. The number of precisely aligned lasers becomes a major challenge when scaling up.

Instead, we are developing a simple electronic gate technology, applying voltages to a microchip in a comparable way to classical transistors and using global microwave fields. This removes the requirement for millions of lasers when we reach the million-qubit scale.

**Modularity matters**

As quantum computers grow, we will eventually be constrained by the size of the substrate you can pattern to make quantum circuits. As such, modularity is key when making scalable quantum computers.

We believe each module must be a self-contained “mini” quantum computer, otherwise, the complexity of the machine will scale significantly with the number of qubits.

If we can create fully integrated self-contained electronic quantum computing modules using silicon technology, then we also benefit from the wealth of expertise in the existing microchip industry.

But, once these modules are made, we need to connect them together. This is a really tricky problem and is seen as a significant obstacle when trying to scale up different quantum computer approaches.

At Universal Quantum, we’ve hit this problem head-on and developed a technique whereby we make use of electric field links that allow our modules to be connected orders of magnitude faster and more reliably than any other approach. This provides an exciting route to scale up.

**All together now**

At Universal Quantum, we are focused on six technology pillars to reach the million-qubit scale. These are (1) mild cooling technology, (2) trapped ion qubits, (3) electronic quantum gates, (4) silicon microchip modules, (5) electric field link modularity and (6) a practical engineering focus. You can read more about each one here.

Of course, the race is far from over as we try to reach the million-qubit scale — and it may not be a two-horse race between superconducting and trapped-ion qubits. Other companies are investigating alternative approaches — and they are all at different levels of maturity.

But we believe that using our unique architecture, trapped ion-based quantum computers are the best bet for making a one-million qubit machine — and it’s an exciting time for us to execute our engineering roadmap and get there as quickly as possible.

To achieve this, scalability in quantum computing cannot exist in isolation. The breadth and complexity of building the world’s first million-qubit machine require interdisciplinary collaboration not only from quantum experts but also from engineering leaders and end-users to get quantum ready and develop a machine that unlocks the true potential of quantum computing to transform the world.

There are lots of exciting announcements on the horizon with our technology. If you’d like to hear the latest news from Universal Quantum about our technology, you can follow us on Twitter & LinkedIn