**By Daniel Lidar, University of Southern California **

The quantum edge is the milestone towards which quantum computing is feverishly working, where a quantum computer can solve problems that are beyond the reach of more 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, opposite set of laws apply. Quantum computers exploit these strange behaviors to solve problems.

There are certain types of problems that are impractical for classical computing to solve, such as breaking state-of-the-art encryption algorithms. Research in recent decades has shown that quantum computers have the potential to solve some of these problems. If a quantum computer can be built that actually solves one of these problems, it will have demonstrated a quantum advantage.

I am a physicist which studies quantum information processing and control of quantum systems. I believe that this frontier of scientific and technological innovation not only promises groundbreaking advances in computing, but also represents a broader surge in quantum technology, including major 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 neither only 1 nor only 0 state 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 the power of quantum computing. Instead, it results in a complex interplay of superposition, intervention and entanglement.

Interference involves manipulating the qubits so that their states combine constructively during computations to enhance correct solutions and destructively to suppress wrong answers. Constructive interference is what happens when the peaks of two waves—such as sound waves or ocean waves—combine to create a higher peak. Destructive interference is what happens when a wave peak and a wave trough combine and cancel each other out. Quantum algorithms, which are few and hard to devise, generate a sequence of interference patterns that give the correct answer to a problem.

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

## Applications of quantum computers

The quantum computer has a number of potential uses where it can outperform classical computers. In cryptography, quantum computers are both an opportunity and a challenge. Most famously, they have it ability to decrypt current encryption algorithmssuch as the widely used RSA scheme.

One consequence of this is that today’s encryption protocols must be re-engineered to be resistant to future quantum attacks. This recognition led to his growing field post-quantum cryptography. After a long process, the National Institute of Standards and Technology recently selected four quantum-resistant algorithms and has begun the process of preparing them so that organizations around the world can use them in their encryption technology.

In addition, quantum computing can dramatically speed up quantum simulation: the ability to predict the outcome of experiments operating in the quantum realm. The famous physicist Richard Feynman envisioned this possibility more than 40 years ago. Quantum simulation offers the potential for major 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 new properties.

Another use of quantum information technology is quantum sense: 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 myriad applications in fields such as; environmental monitoring, geological exploration, medical imaging and surveillance.

Initiatives such as the development of a quantum internet that interconnects quantum computers are critical steps toward bridging the quantum and classical computing worlds. This network could be secured using quantum cryptographic protocols such as quantum key distribution, which enables highly secure communication channels that are protected against computational attacks – including those using quantum computers.

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

## Staying consistent and overcoming mistakes

The field of quantum computing faces significant hurdles in hardware and software development. Quantum computers are particularly sensitive to any unintended interactions with their environment. This leads to the decoherence effect, where qubits quickly degrade to the 0 or 1 states of classical bits.

Building large-scale quantum computing systems capable of fulfilling the promise of quantum speedups requires overcoming decoherence. The key is to develop efficient methods of quantum error suppression and correction, an area in which my own research is focused.

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

## The quantum advantage appears

Quantum computing may one day be as disruptive as its arrival genetic AI. Currently, the development of quantum computing technology is at a critical juncture. On the one hand, the field has already shown early signs of achieving a narrowly specialized quantum advantage. Google researchers and later a team of researchers in China demonstrated quantum advantage to generate a list of random numbers with certain properties. My research group demonstrated a quantum speed-up 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 works to bring quantum edge to products and services in the near future, academic research remains focused on exploring the fundamental principles that underpin this new science and technology. This ongoing basic research, fueled by enthusiastic cadres of young and bright students of the type I meet almost daily, ensures that the field will continue to advance.

**About the Author:**

Daniel LindarProfessor of Electrical Engineering, Chemistry and Physics & Astronomy, *University of Southern California*

This article is republished from The conversation with a Creative Commons license. Read it original article.

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