Richard Feynman posed the subject of whether the quantum world might be replicated by a normal computer in his 1981 lecture Simulating Physics with Computer, as part of a philosophical reflection on quantum theory.
Because quantum variables do not assume fixed values, the difficulty arises from the probabilities associated with quantum states.
They do, in fact, occupy a full mathematical space of potential states at any given instant.
This greatly expands the scope of the computations.
Any traditional computer, Feynman concluded, would be swamped sooner or later.
However, he went on to wonder if this challenge might be handled with a computer that merely calculates state probabilities, or a computer whose internal states are quantum variables themselves.
- The weird quantum features of atomic and subatomic particles would be openly exploited by such a quantum computer.
- Above important, it would have a radically different structure and operation from today's computers' von Neumann architecture.
- It would compute in parallel on the many states adopted concurrently by the quantum variables, rather than processing bit by bit like a Turing computer.
- In a quantum computer, the basic information units are no longer called "bits," but "quantum bits," or "qubits" for short.
- Unfortunately, this term is deceptive since it still includes the term binary, which is precisely what quantum bits are not.
- The nature of information in qubits differs significantly from that of traditional data. Quantum bits, or qubits, are no longer binary, accepting both states at the same time, as well as any values in between.
- As a result, a qubit can store significantly more information than merely 0 or 1.
The unusual capacity of qubits is due to two peculiar qualities that can only be found in quantum physics:
- Superposition of classically exclusive states: Quantum states may exist in superpositions of classically exclusive states. The light switch in the tiny world may be turned on and off at the same time. This allows a qubit to assume the states 0 and 1 at the same time, as well as all states in between.
- Entanglement: Several qubits may be brought into entangled states, in which they are joined in a non-separable whole as though by an unseen spring. They are in some form of direct communication with each other, even though they are geographically distant, thanks to a "spooky action at a distance," a phrase used by Albert Einstein in sarcasm to emphasize his disbelief in this quantum phenomena. It's as though each quantum bit is aware of what the others are doing and is influenced by it.
Superpositions and entanglement were formerly the subject of fierce debate among quantum physicists.
- They've now formed the cornerstone of a whole new computer architecture.
- Calculations on a quantum computer are substantially different from those on a conventional computer due to the radically distinct nature of qubits.
Unlike a traditional logic gate, a quantum gate (or quantum logical gate) represents a basic physical manipulation of one or more (entangled) qubits rather than a technological building block that transforms individual bits into one another in a well-defined manner.
- A particular quantum gate may be mathematically characterized by a matching (unitary) matrix that works on the qubit ensemble's states (the quantum register).
- The physical structure of the qubits determines how such an operation and the flow of information will seem in each situation.
Quantum gates' tangible technological manifestation is still a work in progress.
~ Jai Krishna Ponnappan
You may also want to read more about Quantum Computing here.
