Quantum computing is a fascinating and rapidly evolving field of science and technology that promises to revolutionize many aspects of computing, such as cryptography, artificial intelligence, optimization, simulation and more. Quantum computers use the principles of quantum mechanics to manipulate information in ways that are impossible for classical computers, which rely on bits that can only be in one of two states: 0 or 1. Quantum computers, on the other hand, use something called "qubits" to do their calculations.
What are qubits?
Qubits are like the building blocks of a quantum computer. They are quantum systems that can exist in a superposition of two states, such as the spin of an electron or the polarization of a photon. This means that a qubit can be both 0 and 1 at the same time, until it is measured and collapses to one of the states. Qubits can also interact with each other through a phenomenon called entanglement, which means that their states are correlated even when they are far apart. This allows quantum computers to perform parallel computations on multiple qubits at once, creating a huge advantage over classical computers.
The more qubits a computer has, the more powerful it is. Google's new quantum computer has 70 qubits, which is more than any other quantum computer available today. But qubits are not enough to measure the performance of a quantum computer. Qubits are also prone to errors and noise, which can degrade the quality of the computation. Therefore, another important factor is how well the qubits can be controlled and maintained in a coherent state.
Google's new quantum computer uses superconducting qubits, which are made of metal loops that can carry electric currents without resistance at very low temperatures. These qubits are controlled by microwave pulses and arranged in a two-dimensional grid inside a cryostat, a device that keeps them at near absolute zero temperature. Google has developed advanced techniques to optimize the design, fabrication and calibration of these qubits, as well as to correct and mitigate errors during the computation.
To demonstrate the capabilities of its quantum computer, Google performed an experiment that involved sampling random numbers from a quantum circuit with 53 qubits (the other 17 qubits were not used due to technical issues). This task is very hard for classical computers, because they would have to simulate all the possible states and outcomes of the quantum circuit, which grows exponentially with the number of qubits. Google claimed that its quantum computer completed this task in about 6 seconds, while it would have taken one of the world's best supercomputers, IBM's Summit, about 47 years to do the same.
This achievement is known as "quantum supremacy", which means that a quantum computer can perform a calculation that is practically impossible for a classical computer. Google published its results in Nature in October 2019, after months of speculation and controversy. Some critics argued that Google's experiment was not fair or meaningful, because it used a task that was specially designed to favor quantum computers over classical ones, and that there might be ways to speed up the classical simulation with better algorithms or hardware.
However, Google defended its claim and said that its experiment was an important milestone for quantum computing, showing that quantum processors can outperform classical ones on some tasks, and opening up new possibilities for exploring and developing quantum algorithms for practical problems.
Quantum computing is still in its infancy, and there are many challenges and limitations to overcome before it can become widely available and useful. For example, quantum computers need to scale up to hundreds or thousands of qubits, improve their error correction and fault tolerance capabilities, and find efficient ways to interface with classical computers and networks.
Nevertheless, researchers from Google and other institutions are already working on developing novel quantum algorithms that can help solve near-term applications for various domains.
Google's new quantum computer is an impressive feat of engineering and science that demonstrates the potential of quantum computing to surpass classical computing on some tasks. However, quantum computing is not a magic bullet that can solve any problem faster or better than classical computing. Quantum computing is a different paradigm that requires new ways of thinking, designing and programming. Quantum computing is also a collaborative and interdisciplinary effort that involves researchers from physics, computer science, mathematics, engineering and more. Quantum computing is an exciting and challenging field that offers many opportunities for innovation and discovery.