**Quantum Computing refers to a new form of computation based on quantum physics. It is expected to outperform classical computers in processing data and deriving optimisation from it. This technology can be widely adopted in the environmental sector, including enhancing the performance of energy sources and optimising urban planning. **

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**What is Quantum Computing?**

The classical computers that we use in our daily lives are beneficial to the development of humanity. Yet, these are being slowly substituted by increasingly sophisticated machines.

One problem that classical computers are so bad at solving is optimisation. For instance, how many possible combinations are there to configure the seats of 10 people around a table? The answer is 10, equivalent to about 3.6 million combinations. When the number of seats keeps increasing, the number of possible combinations multiplies. In order to find the optimal arrangement of the seats, we first need a list of criteria that determines the optimal arrangement. However, the most energy- and time-consuming part is that the classical computers need to simulate each combination to generate a result. Depending on the scale of the data, it may take an extremely long time for classical computers to generate a result. Yet, quantum computers have the potential to solve problems in just minutes.

The basic unit of information for classical computers is called a binary digit – also commonly known as ‘bit’. A bit is either “1” or “0”. If there are two bits in a row, there will be four possible combinations – 00, 01, 10, and 11. Therefore, classical computers need to simulate four times to generate a result.

On the other hand, the basic unit of information for quantum computers is called a ‘qubit’. A qubit is not either “1” or “0”. Instead, it exists in a superposition of “1” and “0”. In other words, it is simultaneously a “1” and a “0”. Therefore, two qubits in a row are in a superposition of four states – 00, 01, 10, and 11. Why is it revolutionary? Well, being in a superposition of all states suggests that, theoretically, quantum computers are only required to simulate once to generate a result. It only takes a few attempts to find the optimal arrangement of 10 seats within more than 3.6 million combinations.

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**How is Quantum Computing Related to Environmental Protection?**

Quantum computing can be adopted in any field that requires optimisation; it can be about enhancing the performance of an energy source as well as about developing a smart city where the consumption of energy is minimised.

One example is the quadratic assignment problem (QAP), a mathematical problem that classical computers perform badly. Suppose there are *n* of facilities and *n* of locations, and you are required to configure one facility in each location to minimize the consumption of energy. Logically, if we need to transport frequently a lot of goods between two facilities, we would like to place them closer, and vice versa. A study has compared the performance of a quantum computer and a classical computer in solving the quadratic assignment problem by giving them data from 20 facilities and locations. As a result, the quantum computer generated an accurate answer in about 700 seconds whereas the classical computer failed to do so within the time limit of 12 hours. This study demonstrates the huge potential of quantum computing to optimize urban planning to minimize the consumption of energy.

In addition to its functions, quantum computing by itself is an environmentally friendly technology. According to a study jointly published by NASA, Google, and Oak Ridge National Laboratory, a quantum computer required only 0.002% of the energy consumed by a classical computer to perform the same task. The energy consumed by computers is enormous; not including the energy consumed by normal people’s computers and smartphones, data centres themselves already account for more than 1% of global electricity. If data can be stored in terms of qubits, we can save up a huge amount of energy.

**Current challenges in quantum computing**

The world’s most powerful quantum computer now is the Eagle, developed by the International Business Machines Corporation (IBM) with a capacity of 127 qubits. However, scientists suggest that quantum computers are not commercially useful if their capacity does not reach at least 1,000 qubits. The slow development of quantum computers is mainly due to the technical difficulties in building them.

Scientists are required to manipulate particles as small as electrons in order to make qubits. Electrons need to be maintained in coherence, meaning the state in which the waves of the electrons can coherently interfere with each other. Yet, electrons are highly sensitive to the outside environment, like noise and temperature. Therefore, the manufacturing of qubits is usually done in an isolated environment from the outside world that runs at near absolute zero. Since the movement of atoms is at their lowest state of energy at absolute zero, keeping the electrons at such a temperature helps them to be stable and less affected by the outside environment. This is a way to mitigate the occurrence of decoherence. Yet, we still do not have a clear method to correct decoherence when it occurred because exterior interference may destroy the remaining coherence of other electrons.

Although quantum computing is still at the stage of development, we have already witnessed an enormous improvement in this field since its birth as a theory in the 1980s. Quantum Computing may be the next greatest advancement in humanity, from developing medicines for different incurable diseases by tracking the molecular data of human bodies that classical computers cannot do, to optimising the energy efficiency of cities, countries, and even the world.

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