**Energy Consumption **In the last years, the idea that a quantum advantage should be searched only in a speed-up or in the resolution of problems until now impossible to treat classically has spread, but a very important advantage has been so far almost ignored: quantum computers could possibly provide a significant reduction in terms of the total energy needed to perform a given calculation, and such a lower requirement would translate in a drastic reduction of the footprint of computing. Just to give an idea of what we mean, we try in the following to compare the performances of a quantum and a classical computer. The energy consumption for these devices is estimated through the following expression [1]: **Energy consumption = Operating time × Power use.** In order to compare the performances of a quantum and a classical computer, we base estimations on the (controversial) Google’s quantum supremacy experiment [2]. In this article, Google claims that their superconductive quantum Sycamore processor took about 200 seconds to sample one instance of a quantum circuit a million times, while this task would have needed at least 2.5 days to be completed on the classical Summit supercomputer [3]. Assuming the good approximation of 25 kW of power usage for the quantum computer [1], including the cooling process and all operation electronics, and 13 MW of power usage for the classical counterpart [4], we obtain: Quantum: 0.056 h × 25 kW = 14 kWh, Classical: 60 h × 13,000 kW = 780,000 kWh. In this specific problem, the quantum computation costs **557,000 times less energy** than respect to the classical one. It is worth noticing that even if the calculation would have lasted the same time, the quantum computer would have, anyway, consumed **520 times less energy**. Of course, we still need to wait years to have quantum computers that could be compared to their classical counterparts taking into account the resolutions of different problems, so a significant reduction in the emission-related computation is still years far. Nonetheless, the orders-of-magnitude difference between the energy needed by the two computers makes this a key topic for the climate. **References**: [1] [Quantum technologies for climate change: Preliminary assessment (arxiv.org)](https://arxiv.org/abs/2107.05362v1) [2] [Quantum supremacy using a programmable superconducting processor | Nature](https://www.nature.com/articles/s41586-019-1666-5) [3] [On “Quantum Supremacy” | IBM Research Blog](https://www.ibm.com/blogs/research/2019/10/on-quantum-supremacy/) [4] [US Dethrones China With IBM Summit Supercomputer | Tom’s Hardware (tomshardware.com)](https://www.tomshardware.com/news/us-supercomputer-china-top500-summit,37367.html) #quantum