Quantum Computing

In 2009 “Physics World”, a physics magazine termed the building of first quantum computer as the breakthrough of the year. Since then, there has been much hype over quantum computers and it's computational power referred to as quantum computing. Quantum computing uses quantum phenomenon of superposition and entanglement to perform computation. This area has prompted many physicists and computer scientist to come forward and do research because of great promises it offers over classical computer. Prof. John Morton of University College London says “with 50 qubits you can solve problems beyond fastest super computer today and with 300, you would have more states than there are atoms in the entire universe."

Quantum computers works on the principle of quantum mechanics and behaves differently than a normal computer. Instead of normal bits , it uses qubits to store 0 and 1 values . Qubits are the basic unit of quantum computer and are mostly composed of atoms of silicon, niobium and aluminium. Therefore , in a quantum computer information is stored in qubits . These qubits have some interesting quantum property known as superposition and entanglement. Superposition is the property of the qubit to possess both 0 and 1 states simultaneously without being distinguished before measurement. This is different than the classical computers where a bit can either store 0 and 1 but not both simultaneously both before and after measurement. A qubit remains in superposition of both states unless it is measured. It then collapses to either 0 or 1 state. When two qubits share a non- seperable state they are said to be entangled. ( eg: Bell state in 2 qubit system).

For two qubits sharing an entangled state, the result of measurement in first qubit lets us know the state of the 2nd qubit even before we actually measure it . This holds true only if we are informed about the original entangled state that they shared, however far they are. These two properties of qubits- i.e, superposition and entanglement thus enhances the computational power of quantum computer manifold. For instance, each qubit using superposition can store 2 states (0&1) simultaneously , for n-qubit system it stores 2ⁿ states or computational information . For 500 qubits , we can have 2⁵⁰⁰ different types of information which is much larger than combined multiplication of age of universe in femto seconds and total number of particles present in observable universe . Another use of quantum computation is in the field of molecular stimulation which requires high computational capacity to store information of each molecules and are practically hard on classical computer but can be effectively tackled by quantum computer, like for the visualization of a caffeine structure on a normal computer will need 10⁴⁸ number of 0 &1 to store the information which is equal 10⁴⁸ bits which seems practically impossible but possible with a quantum computer of 160 qubits. Similarly it’s use can be extended to develop more effective drug by analyzing DNA sequencing data and observing the results on a quantum level. Quantum teleportation of information between any large distance without any physical link can be made possible just with a pair of entangled qubits. The quantum phenomenon of superposition and entanglement are exploited to develop algorithm for quantum computer that gives it an computational edge over classical computer. In 1996 , Lov Grover devised an algorithm known as Grover’s algorithm for searching unstructured database using quantum computer . It showed that for an N-item database if a classical computer takes N steps to search , a quantum computer takes √N steps to do the same thing . Hence , it reduces the task efficiently . Another algorithm called Shor’s algorithm invented by Peter Shor in 1994 , aims at finding prime factors to very large integer using quantum properties of qubits.

This task is considered practically impossible for a normal classical computer and could take hundreds of years. This could prove to be a threat to RSA encryption used for securing data during transmission if the Shor’s algorithm works perfectly in quantum computer because RSA encryption works on prime factoring of large integers and someone with knowledge of prime numbers used in integer can only decode the message. Thus, there is need to upgrade our present technologies involving quantum system to meet the challenges of future quantum technology.

But inspite of numerous capabilities of quantum computer discussed earlier, it took a whole lot of hardwork and clever engineering to realize the dream when in 2016, IBM launched it’s first commercial quantum 5-qubit quantum computer and later followed by Google in 2019 with 53-qubit system. The quantum computer is designed in a special way using superconducting coils because to attain superconductivity and 0 state , ultracold temperature of around 0.015 K which is 180 times colder than interstellar space needs to be maintained near quantum circuit with the help of an open dilution system . Moreover, today’s quantum computers are prone to errors due to noise in the lab and quantum decoherence which collapses the state of qubits and make them normal particles. Though lots of improvement works are still ongoing , many of them are in their beginning stages and needs to be revamped continuously in the coming decades to realize our dream of total quantum supermacy – the time when quantum computers will greatly outperform their classical counterpart .