Quantum computing is based on the concept of quantum nature of particles. Instead of just binary digits 0 and 1, quantum computation works on several possibilities a quantum state can have. The basic unit of information in quantum computers is quantum bits or qubits. Any two or more quantum states can be added together superposed and the result will be another valid quantum state, conversely every quantum state can be represented as a sum of two or more other distinct states.
Quantum computing primarily employs two important concepts of quantum physics, superposition and quantum entanglement. In superposition particles are thought of as existing across all the possible states at the same time.However, once a measurement of a particle is made, and for example its energy or position is known, the superposition is lost and now we have a particle in one known state.
Quantum entanglement means that multiple particles are linked together in a way such that the measurement of one particle's quantum state determines the possible quantum states of the other particles even if they separated by several light years. Changing one particle will induce a change in the other.
A 2-bit register in an ordinary computer can store only one of four binary configurations (00, 01, 10, or 11) at any given time, a 2-qubit register in a quantum computer can store all four numbers simultaneously or combination of any two or more configurations because each qubit represents two values,That is a qubit can store a zero, a one, both zero and one, or an infinite number of values in between and be in multiple states (store multiple values) at the same time! If more qubits are added, the increased capacity is expanded exponentially.
It is extremely difficult to get particles to behave in the proper way for a significant length of time. A major difficulty in quantum computing has been any disturbance in a quantum system say a stray photon or wave of EM radiation causes the quantum state to collapse, a process known as decoherence. A quantum computer must be totally isolated from all external interference during the computation phase. Some success has been achieved with the use of qubits in intense magnetic fields, with the use of ions.
Although a fully functioning quantum computer is a longer-term goal, many fundamental and practical discoveries have been made in the name of quantum computing.
A team of NASA and Google engineers announced the D-Wave computer, running an optimization problem, came up with an answer 100 million times faster than a conventional computer with a single core processor. What a D-Wave machine does in a second would take a conventional computer with a single core 10,000 years to perform a similar task.
IBM made a new superconducting chip demonstrates a technique crucial to the development of quantum computers. Google, NASA, Microsoft, IBM, and the U.S. government are all working on this new technology.
