The estimate of needing approximately a million qubits for effective quantum computer physics simulations, as mentioned by Prof. Sabine Hossenfelder, likely comes from considerations based on the complexity of simulating quantum systems and the level of noise in current quantum computers.
Simulating the behavior of quantum systems, particularly those relevant to physics simulations, can be computationally demanding and quickly becomes infeasible for classical computers as the system size increases. Quantum computers have the potential to overcome this limitation by leveraging the principles of quantum mechanics.
However, the noise and errors present in current quantum computers pose challenges for running large-scale simulations. Noisy qubits can lead to errors in quantum computations, limit the achievable coherence times, and degrade the overall performance of the quantum computer.
To effectively simulate quantum physics phenomena with reasonable accuracy, a significant number of qubits may be necessary to overcome the limitations imposed by noise. The specific estimate of a million qubits might be a rough approximation based on current levels of noise and error rates in quantum computers.
It's important to note that the estimate can vary depending on the specific simulation requirements and the desired level of accuracy. The estimate assumes that a sufficient number of qubits are available to encode the quantum state accurately, perform error correction or mitigation, and account for the noise present in the system.
As quantum technology advances and error rates decrease, the number of qubits required for effective simulations may decrease as well. Researchers are actively working on developing error correction techniques, improving qubit coherence, and reducing noise to enable more efficient and accurate simulations on quantum computers.