# Tag Info

Accepted

### Can a Turing machine simulate a quantum computer?

Yes, a quantum computer could be simulated by a Turing machine, though this shouldn't be taken to imply that real-world quantum computers couldn't enjoy quantum advantage, i.e. a significant ...
• 1,457
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### Can a quantum computer simulate a normal computer?

Yes, it can do so in a rather trivial way: Use only reversible classical logical gates to simulate computations using boolean logic (for instance, using Toffoli gates to simulate NAND gates), use only ...

### What are examples of Hamiltonian simulation problems that are BQP-complete?

There are plenty of different variants, particularly with regards to the conditions on the Hamiltonian. It's a bit of a game, for example, to try and find the simplest possible class of Hamiltonians ...
• 47.2k

### What would a very simple quantum program look like?

One way of writing quantum programs is with QISKit. This can be used to run the programs on IBM's devices. The QISKit website suggests the following code snippet to get you going, which is an ...
• 10.6k
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### Classical Memory enough to store states up to 40 qubits quantum system?

Suppose that you have a quantum algorithm with $2^{60}$ possible inputs. Suppose also that it would take 1 nanosecond to run this on a supercomputer (which is unrealistically optimistic!). The total ...
• 10.6k
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### Why doesn't the Gottesman-Knill theorem render quantum computing almost useless?

To my mind, this theorem is not very well stated in this form, if taken out of context. Where it says "phase gates", this may be misleading. It means specifically just $S=\sqrt{Z}$ and not what I ...
• 47.2k
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### How Mature is the Tensorflow Quantum Library

First we should take a step back. Is there any machine learning done a quantum computer that cannot be efficiently simulated on a classical computer? The answer currently (2020) is no. In this ...
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### Can a Turing machine simulate a quantum computer?

To simulate the collapse of the wave function you'd need a source of randomness. So you'd need a probabilistic Turing machine.
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### Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: C29H31N7O?

My quick answer: something between 4 and 4000. ^_^ The number of qubits in an electronic structure calculation depends on at least three things: Your basis set. Your qubit mapping. Your algorithm. ...
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### How to compactly represent multiple qubit states?

There are many possible ways to compactly represent a state, the usefulness of which strongly depend on the context. First of all, it is important to notice that it is not possible to have a ...
• 18.6k
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### Is there any source which tabulates quantum computing algorithms for simulating physical systems?

I believe what you're after is NIST's Quantum Zoo, a comprehensive catalog of quantum algorithms maintained by Stephen Jordan. Its sections include: Algebraic and Number Theoretic Algorithms (14 ...
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### Is there any online Bloch sphere simulator?

This doesn't really answer the question as it's not an online simulator. It might still be relevant though as it is a way to produce this sort of gifs if one has access to the software. It is ...
• 18.6k
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### Is the SWAP gate a Clifford Gate? How would I express it using the Clifford Gate generators?

It's well known that you can make a swap out of three CNOTs. For reference, Stim's gate documentation includes H+S+CX decompositions of a lot of Clifford gates including the swap: ...
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### Is it possible to simulate a quantum computer in Virtual Reality? If yes, how?

Virtual reality in a classical computer is just a fancy front-end on top of a classical simulation. A classical computer can simulate all of the quantum physics happening inside a quantum computer, ...
• 12k
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### What are the preferred numerical methods to simulate the evolution of a state through a time-dependent Hamiltonian?

It depends on the Hamiltonian. There are three particular questions whose answers might influence your choice of strategy: Does the Hamiltonian have any particular structure or symmetry? How quickly ...
• 47.2k

### Are quantum simulators like Microsoft Q# actually using quantum mechanics in their chips?

Quantum simulators don't rely on quantum-mechanical effects in the physical chips; instead they simulate certain aspects of quantum state and operations on it using only classical compute. Universal ...
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