The quantum advantage is the milestone that the field of quantum computing is eagerly working toward, where a quantum computer can solve problems 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, counterintuitive set of laws apply. Quantum computers exploit these strange behaviors to solve problems.
There are certain types of problems that are impractical for classical computers to solve, such as cracking 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 quantum advantages.
I am a physicist studying quantum information processing and control of quantum systems. I believe that this frontier of scientific and technological innovation not only promises breakthrough advances in computation but also represents a broader surge in 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 quantum bit. 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 only 1 nor only 0 is known as a quantum superposition. For each additional qubit, the number of states that can be represented by qubits doubles.
This property is often confused with the source of power in quantum computing. Instead, it is about an intricate interplay of superposition, interference and entanglement.
Interference involves manipulating qubits so that their states combine constructively during calculations to reinforce 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 difficult to design, set up a sequence of interference patterns that provide 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 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 through a quantum computer, enables computational speeds beyond the reach of classical computers.
Applications of quantum computing
Quantum computing has a number of potential uses where it can outperform classical computers. In cryptography, quantum computers present both an opportunity and a challenge. Most famously, they have the potential to decipher current encryption algorithms, such as the widely used RSA scheme.
A consequence of this is that today’s encryption protocols must be reengineered to be resistant to future quantum attacks. This recognition has led to the growing field of 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 world. The famous physicist Richard Feynman envisioned this possibility more than 40 years ago. Quantum simulation offers the potential for significant advances in chemistry and materials science, helping in areas such as the intricate 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 countless applications in areas such as environmental monitoring, geological exploration, medical imaging and surveillance.
Initiatives such as the development of a quantum internet connecting quantum computers are crucial steps towards bridging the quantum and classical computing worlds. This network could be secured using quantum cryptographic protocols such as quantum key distribution, enabling ultra-secure communication channels that are protected against computational attacks – including those using quantum computers.
Despite a growing suite of applications for quantum computing, the development of new algorithms that take full advantage of quantum benefits—especially in machine learning—remains a critical area of ongoing research.
Staying coherent and overcoming mistakes
The field of quantum computing faces significant hurdles in hardware and software development. Quantum computers are highly sensitive to any accidental interactions with their environments. This leads to the phenomenon of decoherence, where qubits quickly decay to the 0 or 1 states of classical bits.
Building large-scale quantum computing systems that can deliver on the promise of quantum speeds requires overcoming decoherence. The key is to develop effective methods to suppress and correct quantum errors, an area that my own research focuses on.
By navigating these challenges, many quantum start-ups and software companies have emerged alongside established tech players such as Google and IBM. This industry interest, combined with significant investment by governments worldwide, underscores a collective recognition of quantum technology’s transformative potential. These initiatives foster a rich ecosystem where academia and industry collaborate, accelerating progress in the field.
Quantum benefits emerge
Quantum computing may one day be as disruptive as the arrival 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 quantum advantages in creating a list of random numbers with certain properties. My research team demonstrated a quantum speedup for a random guessing game.
On the other hand, there is a significant 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 deliver quantum benefits in products and services in the short term, academic research remains focused on investigating the fundamental principles underlying this new science and technology. This ongoing basic research, driven by enthusiastic cadres of new and talented students of the type I meet almost every day, ensures that the field will continue to evolve.
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