tisdag 8 november 2022

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...

2 kommentarer:

  1. Do you have any opinions on Penrose's line of research that for one thing attempts to model how fast collapse happens depending on mass? (I only heard about it on youtube.)

    SvaraRadera