Quantum computing in 2024: The State of Play

Quantum computing in 2024: The State of Play Build • Valentin Macheret • 04/06/24 • 6 min read

Quantum computing is one of tech’s hottest buzzwords right now. But what is it, exactly? Why should we care? And where does the cloud fit in? Have no fear, our in-house expert is here… over to Valentin Macheret, R&D Engineer for Scaleway Labs!

Why does quantum computing exist?

Quantum computing arose from the intersection of two fields: the need for better knowledge about information processing at the quantum level, and the growing need for computing power to solve complex problems such as materials simulation and optimization.

Quantum computing is already vast and will continue to develop over the coming years. Here, we are concerned only with the computational aspect.

One key property of quantum mechanics, superposition, allows a quantum system, such as a photon or an atom, to be in 2 states at the same time. This quantum information-carrying system is called a quantum bit, or qubit , and is the basis of all calculations.

This peculiarity in the qubit enables quantum computers to have tenfold parallelism (doing several things at the same time), making it possible to explore more solutions simultaneously than with binary, bit-based computers.

Imagine having to get out of a maze. In a classical program, you'd sequentially choose left or right at each intersection and keep track of the path taken until you found the exit. In the quantum version of this program, you can explore both left and right at the same time . The time needed to find the solution is exponentially reduced. That's what quantum computing is all about! To find solutions to problems that would be too costly to calculate in the classical way.

Quantum maze

Do such computers really exist? And can they break the algorithm that secures our current communications , RSA-2048 encryption?

State of play and current limits

Yes, quantum computers do exist. But breaking RSA-2048 encryption isn't just around the corner. Let me explain.

All the players building computers (Quandela, IBM, IonQ, Pasqal, DWave...) are focusing on their own technology. Indeed, quantum hardware can be based on many different “quantum support”: photons, superconducting materials, trapped ions, neutral atoms, annealing... Each of these approaches has its own advantages and challenges.

Let's not forget that nothing is simple in this field, and many approaches remain to be explored. Today, it would be pretentious to say which technology will come out on top.

Quantum computer assessment

To qualify the maturity of a quantum computer, we would be tempted to look at available qubits count. But that's only part of the story. In 2000, David Di Vincenzo, an engineer at IBM, proposed a set of 5 criteria for assessing the maturity of a quantum computer.

Here are Di Vincenzo's criteria, and the reality on the ground in 2024:

Di Vincenzo Quantum criteria

Today's major challenges concern the fidelity (i.e. quality) of qubits and the operations applied to them.

To quantify the power of a quantum computer, several metrics arose. These include Quantum Volume (IBM, 2020), which takes into account the number of qubits and their fidelity, or the number of operations per second (IBM, 2021). The reality, however, is that few players are taking the time to measure and publish these metrics, as the priority remains to evolve and enhance the hardware.

Errors are everywhere

One of the biggest challenges facing all quantum computer manufacturers is to reduce the qubits error rate during operations. Errors can be caused by unwanted decoherence, where the state of a qubit can be altered by interaction with the environment (temperature, vibration, acoustic waves, electric fields, etc.), or by simple loss of the quantum support (a photon “lost” in a fiber, for example).

Errors everywhere

This highlights a big paradox in quantum computing: keep isolating qubits from their environment as much as possible... while at the same time keep seeking to control them to perform operations on them.

Two (non-exclusive) solutions stand out: 1) improving hardware to better isolate quantum information from disturbances, and 2) quantum error correction (QEC). Alice & Bob, a French quantum player, takes a mixed approach : creating superconducting qubits with natural resistance to bit-flip, a common type of error.

The key idea behind QEC is simple: use more qubits for information redundancy, and to apply correction operations in the event of errors.

That's why it's important to ask when a new quantum computer is announced: how good is qubit fidelity? How many will I need to use for error correction?

Today, QEC is written manually into the quantum algorithms. It's a tedious task that requires dedicated engineers. QEC can be so cumbersome that it considerably reduces the number of “useful” qubits (information carriers), making it impossible to run certain algorithms.

There are emerging paradigms with incorporated QEC such as measure-based computation (MBQC) or fusion-based computation (FBQC). But these approaches are still theoretical and, to date, no quantum computer has been able to implement them successfully.

So, when will quantum computing be ready ?

Getting back to the RSA-2048 example again, according to this article published in 2021, at least 20 million physical qubits (including correction) would be needed to factor a prime number sufficient to break the protocol. In 2024, there are at best a few hundred qubits on some computers.

An article from 2022 estimates about 372 near-perfect qubits (99.9% fidelity) with a much slower hybrid approach... Prime number factorization estimations are commonplace, we must be cautious in the absence of consensus.

It will take at least another 5-7 years before we reach fault-tolerant quantum computing (FTQC). This transitional period before logical qubits (ie: robust to error) can be used is known as the Noisy Intermediate Scale Quantum (NISQ) era.

The place of quantum emulation in the ecosystem

The key idea behind quantum emulation is simple: use binary power to mimic the behavior of interactions in a real quantum computer (superposition, entanglement, decoherence...). There are emulators that specifically simulate a particular type of hardware (such as Quandela's exQalibur for photonics, or Pasqal's Pulser for neutral atoms).

Almost all emulators offer an error-free mode…