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Technical Insight

Magazine Feature
This article was originally featured in the edition:
Issue 4 2023

A toolbox for photonic quantum computing


A mature integrated photonics platform is essential for building scalable photonic quantum devices. Quantum pioneers can access it by partnering with imec as a technology provider with a flexible CMOS fab.

By Amin Abbasi, Senior Business Development Manager, imec

Will we have a quantum computer one day? There has been a tremendous amount of progress over the last few years – with breakthroughs that were destined to make media headlines. Nevertheless, you’d be hard-pressed to find a quantum expert who’s prepared to give youa 100 percent guarantee that practical quantum computing is already on the horizon.

The main hurdle is scalability. Although physical qubits are essential building blocks of future quantum computers, obtaining them is, more or less, the ‘easy’ part. The more significant challenge is making the necessary connections between thousands or even millions of them. That’s why, in the debate on the preferred method for producing physical qubits, scalability is quickly becoming a decisive argument. It also goes a long way towards explaining why photonics-based quantum computing – a relative newcomer compared with well-established contenders such as superconducting- and semiconductor-based quantum computing – has been attracting much attention lately.

In this article, we look at what makes photonics such a promising match for quantum computing, and we’ll enumerate the existing challenges and how they can be addressed. We also want to highlight imec’s role, not only as an application company for quantum computing using integrated photonics, but also as a technology provider to its valued customers.

Most methods for acquiring qubits require cryogenic cooling, hampering scalability. Source: Getty Images

Harnessing the unshakeable power of photons

Qubits are the primary carriers of information in a quantum computer. In contrast with bits in classical computing, which are constrained to ones or zeros, qubits can be in multiple states simultaneously (ones, zeros and combinations of ones and zeros). String them together, and they contain amounts of information that scale exponentially to astronomical proportions.

Despite this superpower, qubits in their physical form are incredibly delicate. Their decoherence time is very short, meaning that, when you put them in a quantum state, they quickly lose it again. This makes it difficult to do computation, and it
can only be counteracted by cooling them to cryogenic temperatures, preventing interactions with their environment. That’s why the quantum computer prototypes we know so well are surrounded by a roomful of cooling infrastructure, and it partly explains why the scaling challenge is so huge.

There are, however, certain kinds of qubits, such as physical qubits based on near-infrared optical photons, that are less dependent on cryogenic cooling to tens of millikelvins. This is because the energy of optical photons (~ 1 eV) is orders of magnitude larger than the thermal noise at room temperature (~23 meV).

Once you put these photons in a quantum state, they maintain it as long as they can travel freely, potentially making a room-temperature quantum computer more than just a fantasy. But before we can make it a reality, there are plenty of challenges left to solve.