Quantum advantage is the milestone that the field of quantum computing is fervently working towards, where a quantum computer can solve problems beyond the reach of the most powerful non-quantum computers 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 this strange behavior to solve problems.
There are some types of problems that are impractical for classical computers to solve, such as cracking state-of-the-art encryption algorithms. Research over the past 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 any of these problems, it will have provided a quantum advantage.
I am a physicist who studies quantum information processing and control of quantum systems. I believe this frontier of scientific and technological innovation not only promises groundbreaking advances in computation, but also represents a broader wave of quantum technology, including significant advances in quantum cryptography and quantum sensing.
The source of the power of quantum computing
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 a combination of 0 and 1. This state of neither just 1 nor just 0 is known as a 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's power. Instead, it comes down to a complex interplay of superposition, interference and entanglement.
Interference involves manipulating qubits so that their states combine constructively during computations to amplify correct solutions and destructively to suppress the wrong answers. Constructive interference is what happens when the peaks of two waves - such as sound waves or ocean waves - come together to create a higher peak. Destructive interference is what happens when a wave peak and a wave trough meet and cancel each other out. Quantum algorithms, which are sparse and difficult to devise, set up a series of interference patterns that produce the correct answer to a problem.
Entanglement creates a unique quantum correlation between qubits: the state of one cannot be described independently of the other, no matter how far apart the qubits are. This is what Albert Einstein famously dismissed as "spooky action at a distance." The collective behavior of entanglement, orchestrated by a quantum computer, enables computational speeds beyond the reach of classical computers.
Applications of quantum computers
Quantum computing has a range of potential applications where it can outperform classical computers. In cryptography, quantum computers represent both an opportunity and a challenge. Most famously, they have the potential to decipher current encryption algorithms, such as the widely used RSA scheme.
One consequence of this is that current encryption protocols will need to be redesigned to withstand future quantum attacks. This recognition has 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 preparing them so that organizations around the world can use them in their encryption technology.
Furthermore, quantum computing can dramatically accelerate quantum simulation: the ability to predict the outcome of experiments in the quantum realm. Famed physicist Richard Feynman foresaw this possibility more than forty years ago. Quantum simulation offers the potential for significant advances in chemistry and materials science, aiding in areas such as the 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 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 connects quantum computers are crucial steps toward bridging the quantum and classical computing worlds. This network could be secured using quantum cryptographic protocols such as quantum key distribution, allowing ultra-secure communication channels that are protected against computer attacks - including attacks that use quantum computers.
Despite a growing application base for quantum computing, the development of new algorithms that fully utilize the quantum advantage - particularly in the field of machine learning - remains a crucial area of ongoing research.
Stay coherent and overcome mistakes
The quantum computing field faces significant hurdles in hardware and software development. Quantum computers are very sensitive to unintended interactions with their environment. This leads to the phenomenon of decoherence, where qubits quickly degrade to the 0 or 1 state of classical bits.
Building large-scale quantum computing systems that can deliver on the promise of quantum speedups requires overcoming decoherence. The key is developing effective methods for suppressing and correcting quantum errors, an area that my own research focuses on.
In dealing with these challenges, numerous quantum hardware and software startups have emerged, alongside established technology industry players such as Google and IBM. This industry interest, combined with significant investment from governments around the world, underlines a collective recognition of the transformative potential of quantum technology. These initiatives foster a rich ecosystem where academia and industry work together, accelerating progress in this field.
Quantum advantage is in sight
Quantum computers could one day be as disruptive as the advent of generative AI. Currently, the development of quantum computer technology is at a crucial juncture. On the one hand, the field has already shown early signs of achieving a narrowly specialized quantum advantage. Researchers at Google and later a team of researchers in China demonstrated a quantum advantage in generating a list of random numbers with certain properties. My research team demonstrated quantum acceleration for a random number gambling game.
On the other hand, there is a tangible risk that a 'quantum winter' will set in, a period of reduced investment if practical results are not achieved in the short term.
As the technology industry works to achieve near-term quantum advantage in products and services, academic research remains focused on exploring the fundamental principles underlying this new science and technology. This ongoing fundamental research, fueled by enthusiastic cadre of new and smart students of the type I encounter almost every day, ensures that the field continues to develop.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. The Conversation is reliable news from experts. Try our free newsletters.It was written by: Daniel Lidar, University of Southern California.
Read more: Daniel Lidar receives funding from the NSF, DARPA, ARO, and DOE.
