What is quantum computing?

Quantum computing is an emerging technology that follows the laws of quantum mechanicsIt is the study of matter and energy at the atomic and sub-atomic level.. Quantum computing allows problems that were previously considered computationally infeasible to now be solved in a reasonable amount of time.

The underlying architecture of quantum computers varies significantly from traditional computers. It allows them to solve problems exponentially faster than a traditional computer. Traditional computers use bits to perform their operations. However, quantum computers use quantum bits (qubits) to run quantum algorithms.

Qubit

A qubit is the basic unit of information in a quantum computer. It has two states $0$ and $1$, just like traditional computers. Qubits differ from bits because of their ability to exist in a superposition of states $0$ and $1$, until they are measured, which causes the state of the qubits to collapse to one of the two states.

Qubits have some quantum properties like superposition, interference, and entanglement, which helps them outperform their traditional counterparts.

Measurement

Measurement serves as the boundary between the quantum world and the physical world. Measurement causes the qubits to come into the physical world from the quantum world, as qubits collapse into one of the two states. The tricky part is that no one knows why or how the states collapse. This has led to many interpretations like Von Neumann–Wigner, Many-worlds (Everttians), and Copenhagen.

Features

Qubits exhibit multiple features of quantum mechanics. These are explained below:

Superposition

Superposition is the ability of a quantum system to exist simultaneously in more than one state. Each state has a certain probability assigned to it such that the sum of the probabilities of all states equals $1$. In quantum computing, this property allows the qubit to exist in a superposition of $0$ and $1$. Once measured, the qubit collapses to one of the two states, becoming classical in the process.

To understand it further, let's consider a simple example where we take a coin with two sides, head and tail. We then flip the coin into the air and wait for it to land on the floor. It has a 50-50 possibility of being in head state or tail state during the time that it is in the air and on the floor. We can be certain of the state when we look at the coin, also called measurement. This measurement is the end result of the operation. Before the measurement, the coin is in the superposition of the head and tail state.

Superposition exponentially increases the speed of a simulation running on a quantum computer as it can check a vast amount of scenarios at the same time. The final result of the simulation is generated when the qubits are measured, causing the quantum state of the qubits to collapse to one of the two states.

Interference

Interference, also referred to as wave interference, is a phenomenon in which waves superimpose on each other to generate a resultant wave following constructive interferenceConstructive interference occurs when the maxima (crest) of two superimposing waves align together generating a crest of the resultant wave, which is equal to the amplitude of the two crests that superimposed. and destructive interferenceDestructive interference occurs when the maxima (crest) of two superimposing waves are 180 degrees out of phases, meaning crest of one wave overlaps trough of the other wave. This results in an amplitude of zero in the resultant wave..

The concept of interference is relevant in quantum mechanics, as it deals with atomic and sub-atomic particles, and particles behave like waves. However, the concept of quantum interference is a little different compared to wave interference, but the general idea remains the same.

One of the most noteworthy examples of quantum interference is Grover’s search algorithm which amplifies the probability of the desired outcome via constructive interference and diminishes the probability of the undesired outcome(s) via destructive interference.

Entanglement

Quantum entanglement refers to a phenomenon where a pair of qubits are entangled, causing them to exist in the same quantum state even if a huge distance separates them. If the quantum state of one qubit is changed, the quantum state of the other qubit also changes predictably.

Quantum entanglement reduces the computational power required to perform a calculation. Because work done on a qubit allows us to obtain the result of another qubit entangled together. This causes the processing power of a quantum computer to increase exponentially when the number of qubits is doubled.

Quantum computer vs. traditional computer

The differences between a quantum computer and a traditional computer are as given below:

Note: Quantum computers have a high error rate due to a phenomenon called quantum decoherence that is caused by even the slightest vibrations.

Advantages of quantum computing

The advantages of quantum computing are as follows:

• Faster computation: Quantum computer excels in some specialized tasks over a supercomputer. A currently existing quantum computer developed by Google is 158 million times more powerful than a supercomputer.

• Lower power consumption: The power consumption of a quantum computer is less than that of a supercomputer due to quantum tunnelingQuantum tunneling is a phenomenon of quantum mechanics which allows a particle to exist in a state with a non-zero probability that is deemed forbidden in classical mechanics..

• Simulation: As per Richard Feynman’s prediction, quantum computers are more efficient at modeling natural systems at the quantum level and can simulate the dynamics of quantum systems more accurately.

Disadvantages of quantum computing

The disadvantages of quantum computing are as follows:

• Price: Quantum computers are still in the research phase, and the cost of building and operating quantum computers is very high.

• Low operating temperature: They need a very low operating temperature, making them difficult and expensive to operate.

• Internet security: The quantum computers will break current cryptographic protocols like RSA, elliptic curve cryptography, and elliptic curve digital signature algorithm that rely on the internal factorization problem. Therefore, it creates a security threat.

• Error-prone: They are error-prone due to a phenomenon called quantum decoherence.

• Use case: They can not be used for day-to-day use, they are usually better for specific tasks and built according to those requirements, unlike traditional computers which are built for general purpose everyday use.

Applications

Quantum computers are useful in many different fields given as follows:

• Logistics: Quantum computers can relatively easily find the optimal route for trucks and ships compared to a traditional computer.

• Radars: They can be used in radars to detect objects more efficiently and quickly.

• Finance: In finance, quantum computers can be used for prediction, asset trading optimization, and risk profiling.

• Healthcare: They can accelerate the diagnosis process and offer personalized medicine in healthcare. It can also play an important part in creating new drugs as the current process takes a long time because it needs to check how every molecule behaves with the others. Quantum computers can run simulations exponentially faster than traditional computers to speed up this process.

• Climate forecasting: They can forecast weather locally and act as an early warning system for more severe climate threats.