3

I've seen many articles in the popular press saying that quantum computers will enable searching through huge amounts of data in an instant. But I can't figure out how the current architectures can do that at all, things like Google's Sycamore architecture don't even have storage. There is literally nothing to search except for the state space that results from the configuration of the gates (and that seems to be an RF signal that is spread out over time).

So how will quantum computers search anything, other than tuning parameters?

Martin Vesely
  • 15,398
  • 4
  • 32
  • 75
vy32
  • 649
  • 3
  • 14

2 Answers2

2

Qiskit and other programming languages allow to write a hybrid algorithms, i.e. combination of classical and quantum algorithm. Inputs to quantum algorithm can be pre-processed on classical computer and results produced by quantum computers can be post-processed again classically.

You are right that storage is still a problem. So far quantum RAM (qRAM) was proposed. However, it also face problems such a decoherence.

You can find a proposal of quantum RAM architecture here: Quantum random access memory

Some discussion on qRAM is on this forum here.

Overall, data can be stored classically and access via hybrid algorithms. However, in this case part of quantum speed-up is lost.

Martin Vesely
  • 15,398
  • 4
  • 32
  • 75
2

Typically, quantum search algorithm searches through a very large solution spaces that can represented by logarithmic scale of data, not directly over huge amount of data. An example is travelling salesman problem where the input data are the distances between cities, but each solution is a path and the space to be searched is exponential in terms the number of cities.

Nielsen and Chuang’s book suggested two approaches to search really unstructured data directly, by using a quantum memory, or by quantum access to classical memory.

czwang
  • 949
  • 1
  • 6
  • 17