# Tagged Questions

A computation model which relies on quantum-mechanic phenomena, such as entanglement and superposition. This generalizes the probabilistic model of computation.

4answers
116 views

### The difference between a bit and a Qubit

Ok, I have done a lot of research on Quantum computers. I understand that they are possibly the future of computers and may be commonplace in approximately 30-50 years time. I know that a Binary is ...
4answers
177 views

### The physical implementation of quantum annealing algorithm

From that question about differences between Quantum annealing and simulated annealing, we found (in commets to answer) that physical implementation of quantum annealing is exists (D-Wave quantum ...
3answers
105 views

### What is the relation between P vs. NP and Nature's ability to solve NP problems efficiently?

I was thinking about how nature can efficiently compute ridiculous (i.e. NP) problems with ease. For example, a quantum system requires a $2^n$ element vector to represent the state, where $n$ is just ...
1answer
54 views

### Controlled NOT gate a type of measurement?

I'm trying to understand the theory of quantum computing, and I'm a bit confused on a particular circuit: Would the controlled NOT gate be a type of measurement, causing Q1 to be either |0> or |1>, ...
1answer
68 views

### Origin of quantum complexity theory

Who was/were the first person/people to introduce the topic of quantum complexity theory and problem classes like BQP and QMA?
2answers
98 views

### Quantum computing 'amplitudes'

As far as I understand, you receive an output from a quantum computer for an algorithm in the form of an amplitude, which is one of the many states your qubits may be in, however this amplitude is a ...
3answers
150 views

### References on comparison between quantum computers and Turing machines

I was told that quantum computers are not computationally more powerful than Turing machines. Could someone kindly help in giving some literature references explaining that fact?
1answer
83 views

### Help need to learn Quantum Computation and Information

I want to learn quantum computation and information. I am studying from Nielsen & Chuang book for this. Is there any online vedio (lecture series) starts from basics of quantum computation and ...
1answer
62 views

### Tensor Product in Quantum Computation

I can not understand the following equality $$\langle ij|(|0\rangle \langle 0|\otimes I)kl \rangle= \langle i|0\rangle \langle 0|k \rangle \langle j|I|l \rangle?$$ Also to estimate phase $\phi$ in ...
2answers
288 views

### What is the difference between quantum TM and nondetermistic TM?

I was going through the discussion on the question How to define quantum-turing-machines? and I feel that quantum TM and nondetermistic TM are one and the same. The answers to the other question do ...
2answers
147 views

### Organisation and Architecture of Quantum Computers

What are devices and their interconnections used alongwith Quantum Processors? Are they compatible with hardware devices like Cache, RAM, Disks of current computers?
2answers
180 views

### What is the difference between classical crypto and post-quantum crypto?

Will there be a need to change the definitions of security if we have quantum computers? What cryptographic constructions will break? Do you know a survey or an article that explains what will be ...
1answer
313 views

### Quantum lambda calculus

Classically, there are 3 popular ways to think about computation: Turing machine, circuits, and lambda-calculus (I use this as a catch all for most functional views). All 3 have been fruitful ways to ...
2answers
372 views

### Could quantum computing eventually be used to make modern day hashing trivial to break?

Simply put, if one were to build a quantum computing device with the power of, say, 20 qubits, could such a computer be used to make any kind of modern hashing algorithm useless? Would it even be ...
2answers
350 views

### Universality of the Toffoli gate

Regarding the quantum Toffoli gate: is it classicaly universal, and if so, why? is it quantumly universal, and why?
2answers
897 views

### How to define quantum Turing machines?

In quantum computation, what is the equivalent model of a Turing machine? It is quite clear to me how quantum circuits can be constructed out of quantum gates, but how can we define a quantum Turing ...
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