# When will we have a quantum computer?

## TL;DR

This paper discusses the immense complexity of quantum computers with many qubits, emphasizing that controlling their quantum states is the key challenge to realizing practical quantum computing.

## Contribution

It highlights the exponential growth of quantum amplitudes with qubits and frames the control problem as the main obstacle to building scalable quantum computers.

## Key findings

- Quantum state complexity exceeds universal particle count at N=1000 qubits.
- Control of quantum amplitudes is the critical challenge for quantum computer development.
- The difficulty of control grows exponentially with the number of qubits.

## Abstract

At a given moment, the state of the hypothetical quantum computer with N qubits is characterized by 2^N quantum amplitudes, which are complex continuous variables restricted by the normalization condition only. Their values cannot be arbitrary, they must be under our control. For moderate N = 1000, the number of quantum amplitudes greatly exceeds the number of particles in the Universe. Thus the answer to the question in title is: When physicists and engineers will learn to keep under control this number of continuous parameters.