The quantum in “quantum computing” refers to the quantum mechanics that the system uses to calculate outputs. In physics, a quantum is the smallest possible discrete unit of any physical property. It usually refers to properties of atomic or subatomic particles, such as electrons, neutrinos, and photons.

Quantum computing is an area of computing focused on developing computer technology based on the principles of quantum theory (which explains the behavior of energy and material on the atomic and subatomic levels). Computers used today can only encode information in bits that take the value of 1 or 0 restricting their ability. Quantum computing, on the other hand, uses quantum bits or qubits. It harnesses the unique ability of subatomic particles that allows them to exist in more than one state (i.e., a 1 and a 0 at the same time).

According to Gershenfeld, if the current rate of shrinking transistors continues, the width of a wire in a computer chip will be no more than the size of a single atom by 2020. These are dimensions where the laws of classical physics no longer apply. The weird consequences of quantum mechanics will begin to impede the performance of transistors as they become smaller. Richard Feynman, a Nobel Prize-winning physicist, proposed the concept of a “quantum computer” in 1982, a computer that takes advantage of quantum physics’ effects.

For a long time, the concept of a quantum computer was sole of theoretical curiosity, but recent breakthroughs have brought it to the general public’s attention. Peter Shor invented a method to factor huge numbers on the quantum computer, which was one of these breakthroughs (Bell Laboratories). A quantum computer might be able to crack codes significantly faster than a traditional (or classical) computer employing this approach. In reality, a quantum computer capable of running Shor’s algorithm would be able to decrypt contemporary cryptography in a matter of seconds.

The concept of quantum computing has gained traction due to the impetus offered by this technique, and academics worldwide are racing to be the first to build a viable quantum computer. A supercomputer, according to Chuang, takes around a month to find a phone number from a database containing all of the world’s phone books, whereas a quantum computer can complete the operation in 27 minutes. The most successful in the development of quantum computers are the Massachusetts Institute of Technology, Oxford University, IBM, and Los Alamos National Laboratory.

Concepts to Understand Quantum Computing

Quantum computers harness the unique behavior of quantum physics such as superposition, entanglement, and quantum interference and apply it to computing.

Superposition

In superposition, quantum particles are a combination of all possible states. They fluctuate until they are observed and measured. One way to picture the difference between binary position and superposition is to imagine a coin. Classical bits are measured by “flipping the coin” and getting heads or tails. However, if you were able to look at a coin and see both heads and tails at the same time, as well as every state in between, the coin would be in superposition.

Entanglement

Entanglement is the ability of quantum particles to correlate their measurement results with each other. When qubits are entangled, they form a single system and influence each other. We can use the measurements from one qubit to conclude the others. By adding and entangling more qubits in a system, quantum computers can calculate exponentially more information and solve more complicated problems.

Quantum Interference

Quantum interference in the intrinsic behavior of a qubit, due to superposition, influences the probability of it collapsing one way or another. Quantum computers are designed and built to reduce interference as much as possible and ensure the most accurate results. To this end, Microsoft uses topological qubits, which are stabilized by manipulating their structure and surrounding them with chemical compounds that protect them from outside interference.

Qubit

A qubit is the basic unit of information in quantum computing. Qubits play a similar role in quantum computing as bits play in classical computing, but they behave very differently. Classical bits are binary and can hold only a position of 0 or 1, but qubits can hold a superposition of all possible states.

How does it work?

A quantum computer has three primary parts:

• An area that houses the qubits
• A method for transferring signals to the qubits
• A classical computer to run a program and send instructions

For some methods of qubit storage, the unit that houses the qubits is kept at a temperature just above absolute zero to maximize their coherence and reduce interference. Other types of qubit housing use a vacuum chamber to help minimize vibrations and stabilize the qubits. Signals can be sent to the qubits using a variety of methods, including microwaves, laser, and voltage.

Global Quantum Computing Market

The Quantum Computing market is expected to grow from USD 472 million in 2021 to USD 1,765 million by 2026, at a CAGR of 30.2%. The early adoption of quantum computing in the banking and finance sector is expected to fuel the growth of the market globally. Other key factors contributing to the growth of the quantum computing market include rising investments by governments of different countries to carry out research and development activities related to quantum computing technology. Several companies are focusing on the adoption of QCaaS post-COVID-19. This, in turn, is expected to contribute to the growth of the quantum computing market. However, stability and error correction issues are expected to restrain the growth of the market.

Figure 1: Global Quantum Computing Market (Accessible in PDF Version) 

Application Areas of Quantum Computers

Quantum Simulation: Quantum computers work exceptionally well for modeling other quantum systems because they use quantum phenomena in their computation. This means that they can handle the complexity and ambiguity of systems that would overload classical computers. Examples of quantum systems that we can model include photosynthesis, superconductivity, and complex molecular formations.

Cryptography: Classical cryptography such as the Rivest–Shamir–Adleman (RSA) algorithm that is widely used to secure data transmission relies on the intractability of problems such as integer factorization or discrete logarithms. Many of these problems can be solved more efficiently using quantum computers.

Optimization: Optimization is the process of finding the best solution to a problem given its desired outcome and constraints. In science and industry, critical decisions are made based on factors such as cost, quality, and production time all of which can be optimized. By running quantum-inspired optimization algorithms on classical computers, we can find previously impossible solutions. This helps us find better ways to manage complex systems such as traffic flows, airplane gate assignments, package deliveries, and energy storage.

Quantum Machine Learning: Machine learning on classical computers is revolutionizing the world of science and business. However, training machine learning models come with a high computational cost and that has hindered the scope and development of the field. To speed up progress in this area, we are exploring ways to devise and implement quantum software that enables faster machine learning.

Search: A quantum algorithm developed in 1996 dramatically sped up the solution to unstructured data searches, running the search in fewer steps than any classical algorithm could.

The Potential and Power of Quantum Computing

A Quantum computer with 500 qubits gives 2^500 superposition states. Each state would be classically equivalent to a single list of 500 1’s and 0’s. Such a computer could operate on 2^500 states simultaneously. Eventually, observing the system would cause it to collapse into a single quantum state corresponding to a single answer, a single list of  500  1’s and  0’s,  as dictated by the measurement axiom of quantum mechanics.  This kind of computer is equivalent to a classical computer with approximately 10^150 processors.

Integer factorization is believed to be computationally feasible with an ordinary computer for large integers if they are the product of few prime numbers (e.g., products of two 300 – digit primes). By comparison, a quantum computer could efficiently solve this problem using Shor’s algorithm to find its factors. This ability would allow a  quantum computer to decrypt many of the cryptographic systems in use today.  In particular,  most of the popular public-key ciphers are based on the difficulty of factoring integers. These are used to protect secure Web pages,  encrypted email, and many other types of data. Breaking these would have significant ramifications for electronic privacy and security. An example of this is a password cracker that attempts to guess the password for an encrypted file (assuming that the password has a maximum possible length).

Major Difference between Quantum and Classical Computers

A traditional computer’s memory is a string of 0s and 1s, and it can only do computations on one set of numbers at a time. A quantum computer’s memory is a quantum state that can be a superposition of many numbers. A quantum computer can perform any reversible classical calculation on all the numbers at the same time. A quantum computer is far more powerful than a conventional computer because it can perform calculations on many separate numbers at the same time and then interfere with all of the results to get a single response.

Conclusion

The quantum computer’s ability to execute calculations across a myriad of parallel worlds allows it to quickly complete tasks that classical computers will never be able to do. This power can only be unleashed with the right type of algorithm, which is exceedingly difficult to formulate. Some algorithms have already been developed, and they are proving to have enormous ramifications in the cryptography industry. This is because they make it possible to break the most regularly used cryptographic techniques in a couple of seconds. Quantum computers can solve applications that are impossible to solve with today’s computers. This will be one of the most significant advances in science, and it will surely transform the realm of practical computing.