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# Classical vs. Quantum Computing

[RWTH Aachen University, Germany - Martin Braun]

### - Overview

Due to quantum mechanics, quantum computers typically must operate under more regulated physical conditions than classical computers. Classical computers have less computing power than quantum computers and cannot be easily scaled up. They also use different units of data -- classical computers use bits, while quantum computers use qubits.

### - Units of Data: bits and bytes and qubits

In classical computers, data is handled in binary.

Classical computers use bits (a unit of eight bits called a byte) as their basic unit of data. Classical computers write code in binary, either 1 or 0. Simply put, these 1s and 0s represent an on or off state, respectively. They can also indicate true or false, yes or no, for example.

This is also known as serial processing and is sequential in nature, which means that one operation must complete before another completes. Many computing systems use parallel processing, an extension of classical processing to perform simultaneous computing tasks. A classical computer would also return a result because 1 and 0 bits are repeatable due to their binary nature.

However, quantum computing follows a different set of rules. Quantum computers use qubits as units of data. Unlike bits, qubits can have a value of 1 or 0, but can also be 1 and 0 at the same time, existing in multiple states at the same time. This is called superposition, where properties can only be defined after they have been measured.

According to IBM, "superimposed qubits can create complex multidimensional computing spaces," enabling more complex computations. When qubits are entangled, changes in one qubit directly affect the other, which allows for faster information transfer between qubits.

In classical computers, algorithms require massively parallel computing to solve problems. Quantum computers can explain a variety of outcomes when analyzing data with a large number of constraints. Outputs have associated probabilities, and quantum computers can perform more difficult computational tasks than classical computers.

### - The Power of Classical Vs. Quantum Computers

Most classical computers operate based on Boolean logic and algebra, with power increasing linearly with the number of transistors (1s and 0s) in the system. This direct relationship means that in a classical computer, power increases 1:1 with more transistors in the system.

Because a quantum computer's qubits can represent both 1 and 0, the performance of a quantum computer increases exponentially with the number of qubits. Due to superposition, the number of calculations a quantum computer can perform is 2N, where N is the number of qubits.

### - Operating Environment

Classic computers are great for everyday use and normal conditions. Consider something as simple as a standard laptop. Most people can pull their computer out of their briefcase and use it in an air-conditioned coffee shop or on a porch on a sunny summer day. In these environments, performance for normal use, such as browsing the web and sending e-mail for short periods of time, will not be affected.

Data centers and large computing systems are more complex and more temperature sensitive, but still operate at what most people would consider "reasonable" temperatures, such as room temperature. For example, ASHRAE recommends that Class A1 to A4 hardware be kept at 18 to 27 degrees Celsius or 64.4 to 80.6 degrees Fahrenheit.

However, some quantum computers need to reside in tightly regulated and strictly physical environments. Although the first room-temperature computer was recently developed by Quantum Brilliance, some need to be kept at absolute zero, which is around -273.15 degrees Celsius or -459.67 degrees Fahrenheit.

The reason for the cold working environment is that qubits are extremely sensitive to mechanical and thermal influences. Interference could cause the atoms to lose their quantum coherence (essentially the qubit's ability to represent both 1 and 0 at the same time), which could lead to calculation errors.

[More to come ...]