Quantum computing and how it is different from classical computing
Quantum computing harnesses the principles of quantum mechanics to perform calculations in a fundamentally different way compared to classical computers.
Basics of Quantum Computing:
Qubits: Unlike classical bits that can be either 0 or 1, quantum computers use qubits.
These can exist in a state of superposition, meaning they can be both 0 and 1 simultaneously. This allows for parallel processing on a massive scale.
Entanglement: Qubits can be entangled, meaning
they are linked in a way that changes to one instantly affect the other, regardless of their distance.
This enables powerful correlations and computations not possible with classical bits.
Quantum algorithms: These are specially designed instructions that leverage the capabilities of qubits and entanglement to solve problems more efficiently than classical algorithms for certain tasks.
Differences from Classical Computing:
Processing power: While classical computers rely on sequential processing, quantum computers can explore several possibilities simultaneously due to superposition and entanglement.
This makes them potentially much faster for specific problems with numerous variables or combinations.
Problem types: Classical computers excel at tasks with well-defined rules and calculations, while quantum computers shine in problems involving probabilities, complex simulations, and optimizations.
Basic concepts of qubits, gates, and superposition
Gate in computing
A bit is the smallest piece of information storage (it is a portmanteau of binary digit). Often, a large number of bits is required to convey meaningful information.
With the advent of modern semiconductor technology, we routinely speak of household computers having a few terabytes (8 trillion bits) of information storage.
One terabyte can store 500 hours of high-definition video content.
In a computer, a bit is a physical system with two easily discernible configurations, or states – e.g. high and low voltage.
These physical bits are useful to represent and process expressions that involve 0s and 1s: for instance, low voltage can represent 0 and high voltage can represent 1.
A gate is a circuit that changes the states of bits in a predictable way.
The speed at which these gates work determines how fast a computer functions.
The quantum gate
Modern computers use semiconductor transistors to build circuits that function as bits.
A semiconductor chip hosts more than 100 million transistors on 1 sq. mm.
Imagine how small an individual transistor is and how close it is to adjacent transistors.
As transistors become smaller, they become more susceptible to quantum effects.
This is not desirable as the existing technology will then become unreliable for computational tasks.
Moore’s law, announced in 1965, states that computing power increases tenfold every five years.
This law no longer holds as we have already slowed to a two-fold increase every five years.
But this doesn’t have to mean we are nearing the end of computing development: the quantum revolution is coming.
The most basic unit of a quantum computer is a quantum bit, or qubit.
Like in a conventional computer, it is a physical object that has two states.
For example, the spin of a particle can point along two different directions, so the particle can function as a qubit.
Or it can be a superconducting circuit that mimics an atom, and its two states can be a ground state, where it has lower energy, and a higher ‘excited’ state.
Aquantum gateis a physical process or circuit that changes the state of a qubit or a collection of qubits.
In the quantum-computing context, if particles or superconducting qubits are the physical qubits, the gate is often an electromagnetic pulse.
Interlude: Superposition
A fundamental limitation of conventional computing architecture is that each bit can exist in only one of the two states, 0 or 1.
But according to quantum physics, a qubit can also be in a superposition of its two states at the same time.
The basis states of the qubit are similar to the north and east directions.
A qubit in a superposition has some contributions from each basis state.
Different superpositions correspond to different amounts of contributions.
If a qubit is in a superposition, then measuring the qubit will cause it to collapse to one of the two states (i.e. either north or east).
However, we can only predict the probability that it will collapse to one state.
Superposition is one of the main factors responsible for speeding up a quantum computer.
But while superposition provides enormous advantages, it is a fragile effect.
It deteriorates when qubits interact with their environment.
Identifying ways to sidestep or overcome this fragility is an active area of research today.
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