How will quantum computers improve computational power?
Ned Wildgoose Bulloch
The ways quantum computers could enhance the world are exciting. This essay will explain how quantum computers based on quantum gates provide a computational speed-up over classical computers. Then, it will describe some situations where quantum computing could be applied. Computers based on quantum annealing won’t be explored. In classical computers, information is stored in bits – binary digits. These switch between two physical states that represent 1 and 0. 1 Two bits can represent 4 states: 0 0, 0 1, 1 0 and 1 1; 𝑛 bits can represent 2 𝑛 possible values. This involves the binary number system, where each digit’s value is 2 raised to the power of the digit’s place value.
Converting 1010 from binary into decimal Place value: 3 2
1
0
Binary digits:
1
0
1
0
1 × 2 1
1 × 2 3
0 × 2 2
0 × 2 0
Decimal digits:
2 3 + 0 + 2 1 + 0 = 8 + 2 = 10
Decimal Total:
A binary number may represent data such as a memory location or an alphabet character. Programmes are also stored as data, so all computer information can be encoded with enough bits. Running programmes requires many bits to be available at once. Distinct voltage levels or bi-stable devices such as flip-flops are commonly used to implement bits. 2 Quantum mechanics predicts behaviours in small-scale, cold or isolated systems. 3 It’s based on probability theory, with the extension of permitting negative or imaginary probabilities. This defies intuition but fits certain observed effects. 4 These probabilities are also known as amplitudes. 5 Quantum computers rely on qubits – quantum bits – to gain their computational advantages. Qubits make use of quantum superposition, interference and entanglement and are implemented using quantum states such as electron spin. 6
1 Houston-Edwards (2017). 2 Bit (2020).
3 What is quantum computing? (2019). 4 Aarson (2006); Wave function (2020). 5 Aarson (2006). 6 Houston-Edwards (2017); What is quantum computing? (2019); Understanding quantum computers (2020).
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