Corruption of Modern Physics 13: Quantum Computer?

A quantum computer with a few qubits is not small.

Quantum computing is a hype of modern physics supposed to deliver unbounded computing power.  The standard digital computer computes with bits, each taking either the value 0 or 1, while a quantum computer with qubits, each taking the values of two different quantum states in superposition, thus carrying both the value 0 and 1; with bits (1,0) and (0,1), while with qubits (1,1), (1,0), (0,1) and (0,0), thus increasing the number of degrees of freedom from 2 to $4=2^2$, or more generally from $n$ to  $2^n$ which quickly gets huge with increasing $n$.    

Certain operations can be performed on qubit quantum states to form quantum logical gates. Quantum measurement of the state of a qubit destroys the superposition into one of the two states like a projection onto coordinate axes representing probability. Quantum entanglement is supposed to correlate the state of two cubits separated in space. 

It is not known if it is possible to construct a quantum computer capable of performing real tasks of interest. What are then the odds? The idea of superposition of states, like the Schrödinger cat being in superposition of being a bit alive and a bit at the same time, is central. Or an atom in superposition of ground state and excited state. Superposition is an expression of the linearity of the multi-dimensional Schrödinger equation supposed to model atomic physics. But the physical meaning and modeling capacity of a linear multi-dimensional Schrödinger equation is a main unresolved problem of modern physics as made clear in Corruption 3. 

 Key question: Is real atomic physics linear allowing superposition? 

Efforts continue. In particular at Wallenberg Centre for Quantum Technology (at Chalmers my Alma Mater) with the following caveat:

• Unfortunately, there is no simple guide on how to build a quantum computer as it is a very difficult and complex task.

Many cellos as supercomputer

We can compare with a vibrating string governed by a linear wave equation creating after excitation by finger or bow a tone with specific timbre as a superposition of harmonics with different amplitudes. This offers a rich expression of varying timbre from different forms of excitation opening to use the string for some form of computation. The output timbre can be measured through its spectrum in a frequency analysis, while the physics of input excitation of a specific timbre may be difficult to realise. But using a cello as a computer may be easier than building a quantum computer...