According to Moore’s law, transistor count per inch in a dense integrated circuit (IC) doubles every two years. It exponentially increases the computing power while decreasing the relative cost. About 50 years later, Moore’s prediction has reached its physical limits. IBM claims that their 6 nanometres silicon transistor is the world’s smallest working transistor, which indicates that it’s not possible to create smaller circuits anymore. In classical computers, transistors work as electric switches. These switches can block the electricity (movement of electrons) that moves in one direction. As a transistor reaches the size of few atoms, electrons may transfer to the other side of the blocked switch because of a process called quantum tunneling. Classical computers cannot recognize these phenomena at the quantum level, and these technological barriers of classical computing open up a new path for computing based on quantum mechanics.

Tech giants such as IBM, Google, and Microsoft have taken new steps toward quantum computing in recent years. Quantum computers can resolve the processing power limitations encountered in classical computing, and they are even faster than powerful supercomputers. A team of Chinese scientists has claimed that they built a powerful quantum computer nearly 100 trillion times faster than classical supercomputers. These trends show that quantum computing will transform many areas in the future, including material science, healthcare, cybersecurity, communication, finance, and artificial intelligence.

Until the early 80s, quantum computing wasn’t a widely discussed topic in computer science. In 1981, IBM and MIT were co-sponsored a three-day conference titled "Physics of Computation" at Boston, and this conference laid a strong foundation for quantum computing. At that conference, Richard Feynman, a famous theoretical physicist, highlighted the need for quantum computers to simulate quantum computations. Later, he published a paper titled "Simulating Physics with Computer" regarding the subject. Paul Benioff, a physicist who researched quantum information theory, first demonstrated a quantum mechanical model of a computer.

What is quantum computing?

Quantum computers make use of principles of quantum mechanics to process information. These computers are fundamentally different from classical computers such as laptops, PCs, smartphones, and supercomputers. Quantum computing primarily bases on vital quantum principles such as superposition and quantum entanglement. The bit is the smallest unit of data in classical computers that stores a single binary value, either 1 or 0, which corresponding to the electrical values on and off. In quantum computers, a quantum bit or qubit known as the basic unit of data. 

Google quantum computer. Image source: cnet

Qubit

Qubits are subatomic particles such as electrons or photons and fundamental building blocks of quantum computers. Unlike bits in classical computers, qubits can exist in two states simultaneously, both 0 and 1. This arrangement of qubits is known as the quantum superposition. As a qubit is measured, this superposition will immediately collapse to either 0 or 1. For instance, an electron that spins along the z-axis can position in both an up or down state simultaneously. When we try to measure the spin of an electron, it will change either to an up or downstate. Using two bits, it can create four binary combinations 00, 01, 10, and 11. In classical computing, to represent one of these combinations requires two bits. But, in quantum computing, two qubits are enough to represent all four combinations simultaneously. It makes quantum computers more powerful than classical ones.

Quantum entanglement

Entanglement is the key quantum effect that enables massive computational power in quantum computers. In entanglement, the state of one quantum particle (qubit) inextricably binds to the state of another particle, and both particles are in an entangled state. Any changes to the state of one qubit will instantly change the state of the other qubit predictably, even the qubits separated by a large distance. That’s what Einstein called “The spooky action at a distance.” It’s impossible to explain how the entanglement works. But, after many experiments, now scientist know that this is how quantum entanglement works.

Decoherence

The entangled state of qubits is very fragile and can easily destroy from interferences of the environment. It’s known as decoherence.  The state of qubits needs to know before running an algorithm in a quantum computer as it determines the algorithm's results. But, the state of entangled qubits can change unnoticeably because of various factors such as vibrations, temperature fluctuations, air molecules, electromagnetic waves, collision with other particles, and interferences from the outside environment. Without knowing the actual state of qubits, it cannot trust the results that the algorithm returned. Even observation could change the quantum properties. To stabilize the qubits' state, quantum computers need to keep under extremely low temperatures close to absolute zero (-273°C) with low atmospheric pressure and insulate from the earth’s magnetic field. Therefore, future advancements in quantum computing should focus on creating quantum computers that can be operated in normal environments while preserving coherence.

Quantum supremacy

Quantum supremacy is the potential ability of quantum computers to solve a problem that classical computers cannot solve in a reasonable time frame. This term was first introduced by John Preskill, a theoretical physicist, in 2012. In October 2019, Google scientists claimed that their 54-qubit Sycamore processor had surpassed the classical computers and achieved quantum supremacy for the first time. In December 2020, a group of Chinese scientists at USTC stated that their photonic quantum computer named Jiuzhang performed a computation called “Gaussian boson sampling” in 200 seconds that a classical supercomputer would require 600 million years to complete.

Though quantum computers achieved quantum supremacy, classical computers still have some unique properties that quantum computers cannot acquire. For instance, quantum computers cannot give straightforward outputs as classical computers do. However, quantum computers have proven their usage in complex algorithms, optimization problems, data analysis, and simulations.

Quantum computing use cases

Quantum computers are open up new opportunities for a wide range of industries. These are some industries that would massively benefit from quantum computing.

Finance

Financial institutions expect to run quantum algorithms to increase the efficiency and eventually the income of their businesses. For instance, the Royal Bank of Scotland has used a quantum algorithm developed by 1QBit to reduce the time taken for loan-related calculations from weeks to seconds. Quantum computing also allows businesses to improve areas include uncertainty in decision making, portfolio optimization, and fraud detection.

Artificial intelligence & Machine learning

Artificial intelligence and Machine learning are two important areas that expect to expand with quantum technologies. Quantum computing will be deeply beneficial to AI because of its ability to process a large number of complex datasets in less time. Quantum algorithms can also use to enhance machine learning capabilities. A new type of ML discipline known as Quantum Machine Learning (QML) emerges with quantum computing.

Healthcare

Quantum computing could accelerate the research on drugs and treatments. Drug development is a challenging and expensive process because of its trial and error approach. Researchers believe that quantum computers could deploy to perform silico clinical trials to understand the drugs and their reaction to humans. Quantum computing enables faster genomic analysis that will streamline personalized medicine practices.

Cybersecurity

Quantum computing could raise the risk factors in cyber-security by breaking the current public key encryptions. But, it also creates new opportunities to strengthen cybersecurity in the quantum era. Researchers have developed new cryptographic algorithms called Post-quantum cryptography (PQC) to secure against the threats from quantum computers. Quantum key distribution (QKD) uses properties of quantum mechanics to exchange encryption keys between shared parties.

Logistics

Optimization, one of the key capabilities of quantum computing, has the potential to transform the logistic industry forever. Logistics companies predict that optimized data analysis and modeling capabilities in quantum computing will enhance the supply-chain management processes such as dynamic route optimization, simultaneous packaging, re-planning, and reallocation of assets.