Computers are getting smaller and faster day by day because electronic components are getting smaller and smaller. But this process is about to meet its physical limit.

Electricity is flow of electrons. Since size of transistors is shrinking to size of few atoms, transistors cannot be used as switch because electron may transfer themselves to the other side of blocked passage by the process called quantum tunnelling.

**Quantum mechanics** is a branch of physics that explores physical world at most fundamental level. At this level particle behave differently from classical world taking more than one state at the same time and interacting with other particles that are very far away. Phenomena like superposition and entanglement take place.

**Superposition –**

In classical computing bits has two possible states**either zero or one**. In quantum computing, a qubit (short for “quantum bit”) is a unit of quantum information—the quantum analogue to a classical bit. Qubits have special properties that help them solve complex problems much faster than classical bits. One of these properties is**superposition**, which states that instead of holding one binary value (“0” or “1”) like a classical bit, a qubit*can hold a combination of “0” and “1” simultaneously*. Qubits have two possible outcomes zero or one but those states are superposition of zero and one. In quantum world qubit don’t have to be in one of those states. It can be in any proportion of those states. As soon as we measure its value its has to decide whether it is zero or one. This is called superposition. It is the ability of the quantum system to be in multiple states at same time.In classical computing for example there are 4 bytes. The combination of 4 bytes can represent 2^4=16 values in total and one value a given instant. But in a combination 4 qubits all 16 combination are possible at once.

**Entanglement –**

Entanglement is an extremely strong correlation that exists between quantum particles — so strong, in fact, that two or more quantum particles can be linked in perfect unison, even if separated by great distances. The particles remain perfectly correlated even if separated by great distances. Two qubits are entangled through the action of laser. Once they have entangled, they are in an indeterminate state. The qubits can then be separated by any distance, they will remain linked. When one of the qubits is manipulated, the manipulation happens instantly to its entangled twin as well.

**What can quantum computers can do?**

- Quantum computers can easily crack the encryption algorithms used today in very less time whereas it takes billions of years to best supercomputer available today. Even though quantum computers would be able to crack many of today’s encryption techniques, predictions are that they would create hack-proof replacements.
- Quantum computers are great for solving optimization problems.

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