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## How Do Quantum Computers Work?

Normal Computer: Transistors → Logic Gates → Modules → Computer Chips

• Transistors are electric switches that open and close the gate for electrons to pass
• A typical transistor is 14 nanometers (500x smaller than a red blood cell)
• Once transistors get down to the size of a few atoms, electrons might bypass the transistors’ barriers via Quantum Tunneling
• Logic Gates receive 1 set of inputs and produce 1 definite output
• Quantum Gates manipulate an input of superpositions, rotates possibilities, and produces another superposition as its output
• Quantum Computer: Qubits → Quantum Gates → Modules → Computer Chips
• Due to Superposition, one set of inputs can result in all possible outputs
• Due to Entanglement, Quantum Gates can be manipulated to choose the desired output

While normal computers use bits as the smallest unit, quantum computers use qubits.

Qubits, Superposition, and Entanglement

• Qubits can be set to one of two values (ex. vertically vs horizontally polarized)
• At any given moment qubits can be both vertically and horizontally polarized (60/40 for example) because of Superposition
• But once the qubits are passed through a filter it must choose one or the other (double slit experiment)
• The outermost electron in a Phosphorus atom is often used as a qubit
• Electrons have magnetic fields, a property called spin, and will align with the field like a compass
• Spin Down: lowest energy state where the electron is naturally aligned with the magnetic field
• Spin Up: highest energy state where the electron is aligned opposite to the magnetic field
• Due to Superposition, qubits can store exponentially more information than bits
• 4 bits can have 24 combinations of 0s and 1s, user can choose to represent 1
• 4 qubits can have 24 combinations, and it can be all 16 at the same time
• 20 qubits can store over 1 million combinations at once
• Each qubit reacts to a change in the other’s state instantaneously regardless of distance from each other because of Entanglement
• Allows us to deduce the state of another qubit by measuring the state of one qubit

To conclude: a quantum computer is not faster than a traditional computer in every way, it is a computer where the number of operations required to arrive at the result is exponentially smaller.

Roadblock to Quantum Computers

• Qubits will only stay in superposition under very strict conditions
• No radiation, no quantum vibrations, kept in temperatures just above absolute zero, etc.
• Most are only able to maintain qubit superposition for a few seconds so far

Applications: Solving NP-Complete Problems

• Database searching (takes the square root of normal computing time)
• Key encryption/decryption (probability trial and error)
• Simulations (drug discovery and molecular mapping)
• Weather patterns (modeling climate change)
• AI training (data labeling for ANN)

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