*Quantum computing is the next holy grail of computer science and engineering, promising to change everyday life for the better.*

Today’s smartphones have the same computing power as a military computer 50 years ago that was the size of an entire room. Yet despite the phenomenal strides we have made in technology and computing, there are problems classical computers just can’t solve. Under the hood, a classical computer is really just a sequence of bits — 0s and 1s.

A quantum computer is different because its bits, called qubits, can be 0 and 1 at the same time — mimicking how atomic and subatomic particles can exist in more than one state at a time. This ability is called “quantum superposition.” While a classical bit can store only 0 or 1, a qubit can have a state of both 0 and 1 simultaneously. Imagine a sphere as depicted by the Bloch sphere. A bit can be at either of the two poles of the sphere, but a qubit can exist at any point on the sphere. Thus, qubits can store an enormous amount of information while using less energy than a classical computer.

Another property is “quantum entanglement.” This is a physical phenomenon that means that a quantum state must be described for the system as a whole, not for individual qubits. One application of entanglement is cybersecurity. With entanglement, it is easy to create one-time pads that create encryption keys in completely randomized environments, thereby foiling even sophisticated hacking attempts.

## Solving complex problems

Quantum computers are not intended to replace classical computers; instead, they are expected to be a different tool used to solve complex problems that are beyond the capabilities of a classical computer.

Two fundamental quantum algorithms, Grover’s and Shor’s algorithms, show us what a quantum computer can do:

**Grover’s Algorithm (GA).**This algorithm perfectly demonstrates the capabilities of a quantum computer. Suppose you are given an*unsorted*list of “N” items. To search for an item in this list, a classical computer would take on average N/2 searches, and in the worst case “N” searches if the item is in last place or not on the list. GA, on the other hand, takes only √N searches! If a list has 1 billion items, then GA would require only √(1 billion) = 31,623 searches. That compares to ~500,000,000 for a classical computer.**Shor’s Algorithm.**Although any integer number can be broken down into a product of prime numbers, finding the prime factors is believed to be a hard problem. In fact, the security of our online transactions rests on the assumption that factoring integers with a thousand or more digits is practically impossible. This assumption was challenged when Peter Shor proposed a polynomial-time quantum algorithm for the factoring problem. Shor’s algorithm is arguably the most dramatic example of how the paradigm of quantum computing changed our perception of which problems should be considered tractable.

## Molecule simulation

Molecule simulation is another game-changing application of quantum computing. Chemical reactions are quantum in nature, because they form highly entangled quantum superposition states. While the energies of molecular hydrogen can be computed classically (albeit inefficiently), working out the energy of something like a propane (C3H8) molecule would take a classical supercomputer on the order of 10 days. With a quantum computer it would take just minutes. Molecule simulation has enormous potential in chemistry, with benefits ranging from better solar cells to new medicines.

At DXC Labs we have implemented Grover’s and Shor’s algorithms on IBM’s Quantum Experience platform, with both online and local simulators along with Python. We have run molecule simulations of Hydrogen and Lithium Hydride using the Microsoft Quantum Development Kit with Q# and C#.

## Changing our world

By entering the quantum arena, where the traditional laws of physics no longer apply, we will be able to create quantum processors that are significantly faster (by a million times or more). This will have a huge impact on the way we do business, invent new medicines and materials, safeguard our data, explore space, and predict weather events and climate change.

It’s no coincidence that some of the world’s most influential companies and governments are investing in quantum computing technology. They are expecting quantum computing to change our world because it will allow us to solve problems and experience efficiencies that aren’t possible today.

**Vaidyanathan Sivasubramanian** is a technologist at DXC Labs and chief technology officer for a large energy account. Vaidya is deeply passionate about technology and constantly dabbles with emerging technologies. He has over 27 years of IT experience and has worked with various Fortune 50 companies. Connect with Vaidya on LinkedIn to see a few of his projects.

Excellent Vaidya! Great Information!