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The quantum advantage is the milestone that the field of quantum computing is feverishly working towards, where a quantum computer can solve problems that are beyond the reach of the most powerful non-quantum, or classical, computers.

Quantum refers to the scale of atoms and molecules where the laws of physics as we experience them break down and a different, counter-intuitive set of laws apply. Quantum computers take advantage of these strange behaviors to solve problems.

There are some types of problems that are impractical for classical computers to solve, such as breaking state-of-the-art encryption algorithms. Research over the past few decades has shown that quantum computers have the potential to solve some of these problems. If it is possible to build a quantum computer that actually solves one of these problems, it will have demonstrated quantum advantage.

I am a physicist who studies quantum information processing and the control of quantum systems. I believe this frontier of scientific and technological innovation not only promises groundbreaking advances in computing, but also represents a broader rise in quantum technology, including significant advances in quantum cryptography and quantum sensing.

## The source of quantum computing power

Central to quantum computing is the quantum bit, or qubit. Unlike classical bits, which can only be in states 0 or 1, a qubit can be in any state that is some combination of 0 and 1. This state of neither just 1 nor just 0 is known as quantum superposition. With each additional qubit, the number of states that can be represented by the qubits doubles.

This property is often confused with the source of quantum computing power. Instead, it all comes down to an intricate interplay of superposition, interference, and entanglement.

Interference involves manipulating qubits so that their states combine constructively during calculations to amplify correct solutions and destructively to suppress wrong answers. Constructive interference is what happens when the peaks of two waves – like sound waves or ocean waves – combine to create a higher peak. Destructive interference is what happens when a wave peak and wave trough combine and cancel each other out. Quantum algorithms, which are few and difficult to devise, establish a sequence of interference patterns that produce the correct answer to a problem.

Entanglement establishes a unique quantum correlation between qubits: the state of one cannot be described independently of the others, no matter the distance between the qubits. This is what Albert Einstein dismissed as “spooky action at a distance.” The collective behavior of entanglement, orchestrated through a quantum computer, enables computational speedups that are beyond the reach of classical computers.

## Applications of quantum computing

Quantum computing has a range of potential uses where it can surpass classical computers. In cryptography, quantum computers represent both an opportunity and a challenge. Most famously, they have the potential to crack current encryption algorithms such as the widely used RSA scheme.

One consequence of this is that current encryption protocols need to be redesigned to be resistant to future quantum attacks. This recognition led to the burgeoning field of post-quantum cryptography. After a long process, the National Institute of Standards and Technology recently selected four quantum-resistant algorithms and began the process of preparing them so that organizations around the world can use them in their encryption technology.

Furthermore, quantum computing can dramatically speed up quantum simulation: the ability to predict the outcome of experiments that operate in the quantum domain. The famous physicist Richard Feynman imagined this possibility more than 40 years ago. Quantum simulation offers the potential for considerable advances in chemistry and materials science, aiding in areas such as complex modeling of molecular structures for drug discovery and enabling the discovery or creation of materials with novel properties.

Another use of quantum information technology is quantum sensing: detecting and measuring physical properties such as electromagnetic energy, gravity, pressure, and temperature with greater sensitivity and precision than non-quantum instruments. Quantum sensing has numerous applications in areas such as environmental monitoring, geological exploration, medical imaging and surveillance.

Initiatives such as the development of a quantum Internet that interconnects quantum computers are crucial steps in bridging the worlds of quantum and classical computing. This network could be secured using quantum cryptographic protocols, such as quantum key distribution, which allows for ultra-secure communication channels protected against computational attacks – including those using quantum computers.

Despite a growing set of applications for quantum computing, the development of new algorithms that fully take advantage of the quantum advantage – particularly in machine learning – remains a critical area of ongoing research.

## Stay consistent and overcome mistakes

The field of quantum computing faces significant obstacles in hardware and software development. Quantum computers are highly sensitive to any unintended interactions with their environments. This leads to the phenomenon of decoherence, where qubits rapidly degrade to the 0 or 1 states of classical bits.

Building large-scale quantum computing systems capable of delivering on the promise of quantum acceleration requires overcoming decoherence. The key is to develop effective methods for suppressing and correcting quantum errors, an area on which my research is focused.

In facing these challenges, numerous quantum hardware and software startups have emerged alongside well-established technology industry players such as Google and IBM. This industry interest, combined with significant investment from governments around the world, underscores a collective recognition of the transformative potential of quantum technology. These initiatives foster a rich ecosystem where academia and industry collaborate, accelerating progress in this field.

## Quantum advantage appearing

Quantum computing could one day be as disruptive as the arrival of generative AI. Currently, the development of quantum computing technology is at a crucial juncture. For one thing, the field has already shown early signs of having achieved a narrowly specialized quantum advantage. Researchers at Google and later a team of researchers in China demonstrated quantum advantage in generating a list of random numbers with certain properties. My research team demonstrated a quantum speedup for a random number guessing game.

On the other hand, there is a tangible risk of entering a “quantum winter”, a period of reduced investment if practical results do not materialize in the short term.

While the technology industry is working to deliver quantum advantages in products and services in the near term, academic research remains focused on investigating the fundamental principles that underpin this new science and technology. This ongoing basic research, fueled by enthusiastic cadres of bright new students of the kind I encounter almost every day, ensures that the field will continue to progress.