A quantum computer works on the quantum states of matter to perform processing and storage operations on data. It differs from classical computing algorithms in the way in which data is considered. Conventionally data is expressed as binary in the computing world: 0 and 1. By manipulating the voltage supplied to silicon chip to maintain its excitation status either at 0 or 1, it is possible to perform complex calculations and store terabytes of data with semiconductor atoms. But the quantum world out there is a crazy one in which a particle can exist at two distinct locations simultaneously. A tennis ball served from one end cannot split into two balls and simultaneously follow two distinct paths, but an electron can! That makes it possible to manipulate these subatomic particles to exist at 0 and 1 or any intermediate state at the same time.
So if it is possible to retain a particle simultaneously at 0 and 1 or intermediate states, multiple operations can be performed all along these intermediate states and can used as a medium to store large volume of data. This superposition of binary bits in quantum computing terminology is called as ‘qubit’. Qubits can be of atoms, electrons, photons and ions working to perform mathematical and storage operations in quantum world.
Parallelism and entanglement are two important concepts which are relevant exclusively for quantum computing. Parallelism refers to simultaneous performance of operations on qubits, which indicates very high processing speed and storage memory. But measuring a particular state of a particle at a particular instant is tricky. Supplying an external force to read a state disturbs it and makes the particle acquire a new state. So the concept of quantum entanglement is used to identify the current state. In quantum science two atoms can be made to entangle with each other by supplying a certain force, and the second entangled atom has the same properties as the first one. As an illustration, let us consider the case of a normal undisturbed atom rotating in any random direction. When it is entangled with another atom, the rotation changes and the second atom has exactly opposite direction as the first one. This aspect of Pauli’s exclusion principle serves our purpose in quantum computing. By supplying a source of entanglement with the qubits, they can be measured without directly contacting them.
Ions or atoms spatially suspended using electromagnetic fields are one important means of building a quantum computer. These trapped ions are used as qubits to hold information and transfer of this information is achieved through laser coupling. Performing logical operations on these qubits is done using quantum gates, similar to the concept of binary logic gates used in digital computing. While logic gates are operated by just varying voltages on a silicon chip, quantum gates require extensive laser interaction arrangements to flip the atomic states. There are some predefined quantum gate schemes for which laser is used to couple the internal qubit states to perform the desired operation. This works well for a small system with few qubits, but for a large working quantum computer, huge number of precisely aligned laser beams would be required to build the quantum gates.
Recently a team from University of Sussex, Imperial College London and The Hebrew University of Jerusalem developed a quantum computing system similar to a digital computing one: using electrical voltage instead of laser. In their paper “Trapped-Ion Quantum Logic with Global Radiation Fields”, they proposed a solution of applying controlled voltages to the gate zones where operations are to be done. Irrespective of the number of ions used in the computer, only a handful of global radiation fields are required for the number of gate zones employed. So building a multiple-qubits quantum computer is not far from reach.
Managing huge databases and retrieving required data becomes very simple through quantum computing. They can be used to unearth unknown phenomena in the quantum scale in science and engineering. But that doesn’t come without a cost. Our existing encryption networks work with apparently unbreakable algorithms as per present computing standards. With the abilities of quantum computers, applying brute force attack and cracking secret passwords would also become child’s play. So it is inevitable to rewrite the security algorithms to counter quantum threats, maybe again by using quantum algorithms.
D-Wave, a Canadian startup has already demonstrated capabilities of making practical quantum computing a reality. It uses a superconducting processor in tiny lattices at absolute zero temperature to obtain the needed quantum effects. Working with the objective to understand everything from universe to human DNA, they seek answers for problems unsolvable by the most sophisticated supercomputers. Sure we are stepping into the next computing era where our PCs might become QCs one day.