Questions tagged [classical-computing]
For questions about the relation between quantum computing and classical computing, such as their relative performance.
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Where is "quantum search" in the complexity hierarchy?
Grover's algorithm is one of the most popular quantum algorithms that solves the problem of "quantum search." But what is this problem, and what are its characteristics.
When considering ...
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Is there something wrong with cross-entropy benchmarking, or is it still considered as a reasonable path towards quantum supremacy?
My question is strongly related with this one. Google's quantum supremacy claim uses Random Circuit Sampling. The principle is the following one: a realistic noise model for random circuits performed ...
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How does one convert a truth table to a square permutation matrix?
Given a classical circuit of $m$ inputs and $n$ outputs, composed of various AND gates, OR gates, NOT gates, etc., a truth table is a $2^{m}\times(m+n)$-sized matrix, where, in general, the first $m$ ...
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Applying a clock in quantum computing?
In quantum computing, I feel it mostly looks like designing hardware with Hardware Description Language (HDL) experience such as VHDL or Verilog.
So the term program language for quantum computing ...
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Why do people say that Grover's algorithm does not parallelize well?
I've seen several sources, including NIST, claim that Grover's algorithm is unlikely to be useful for attacking a symmetric-key algorithm like AES-128 or a hashing algorithm because "Grover's ...
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Why do computer scientists care about the phase of qubits?
When I design some classical register, flip-flop, binary counter, small byte of RAM, etc from scratch with classical logic gate, I never deal with such binary direction because classical bit doesn't ...
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Mapping a classical cipher into quantum implementation of Grover Oracle
I am translating simple ciphers into quantum implementation in order to create oracle for Grover algorithm. I have started the task with a light weight SPECK cipher (got both classical and quantum ...
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Can there be an equivalent classical circuit for a quantum circuit?
It is known that any classical circuit or algorithm can be implemented on a quantum computer using universal quantum gates. My question is, can there be a circuit with classical statistics which are ...
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Is there any real world problem where I can see quantum computing being better than classical computing?
Is there any paper or piece of code showing, on a REAL quantum computer, that a specific real world problem (possibly related to computer science, machine learning or finance and possibly NOT related ...
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What are the practical advantages of quantum GANs with respect to classical ones?
I read some papers on Quantum GANs, for instance this one and this one. I also noticed all the main quantum computing frameworks have a tutorial on quantum GANs, e.g. qiskit.
However I don't really ...
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Accuracy of Classical Counting problem
Consider a classical algorithm for the counting problem which samples uniformly and
independently $k$ times from the search space, and let $X_1, ... ,X_k$ be the results of
the oracle calls, that is, $...
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Why does having two classical registers sometimes only yeild one bit?
I was running some qiskit code on qasm_simulator to test something and I realized that, when I have two separate classical registers, sometimes only one bit is generated, and I'm trying to understand ...
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How does Fujitsu's digital annealer work?
I have read Fujitsu's white paper for a brief introduction to their device:
http://marketing.us.fujitsu.com/rs/407-MTR-501/images/quantum-inspired-computing.pdf
As far as I know, Fujitsu's hardware is ...
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determine degree of boolean polynomial given as black box
I searched a lot but couldn't find a good resource that addresses this question. Given a boolean polynomial with $n$ boolean variables as a black box, what is the most efficient way to compute its ...
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Are qubits just analog, continuous classical bits? [duplicate]
Topologically, classical bits (cbits) are essentially special cases of qubits restricted to the poles of the Bloch sphere. However, this restriction doesn't seem to be classical per se, but is simply ...
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Best classical algorithm for period finding on finite Abelian groups
Given a finite Abelian group $G = \prod_{j=1}^n \mathbb{Z}_{m_j}$ with $m_j \geq 2$ and a function $h: G \to \mathbb{C}$ that is $s$-periodic. I have already proven that for all $\xi \in G$ we have $\...
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Would the interest in building quantum computers decrease if a classical algorithm for factoring all integers in polynomial time is discovered?
Quoting Wikipedia:
No algorithm has been published that can factor all integers in polynomial time, that is, that can factor a $b$-bit number $n$ in time $O(b^k)$ for some constant $k$. Neither the ...
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Will standard programming languages be applicable for quantum computing?
I'm new to quantum computers and computing, so it's possible my question is pointless or unnecessary ... but what about current programming languages such as Java, C++, Python in terms of quantum ...
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Circuit from finite group of gates and classical simulations
Let $ G $ be a finite group of quantum gates. Is it true that any circuit made using only gates from the finite group $ G $ can be efficiently simulated on a classical computer?
Here by circuit made ...
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Can a Hankel matrix $H$ be efficiently decomposed into a linear combination of unitaries (LCU), so that $H=\sum_k a_k U_k$
Suppose I have a Hankel matrix of arbitrary size $N\times M=2^n\times 2^m$ for integers $n<m$ (the qubit numbers of two circuits I have at my possession), given by:
$H=\begin{pmatrix}x_1&x_2&...
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What is the relationship between the size of the Hilbert space for boson sampling and the complexity of classical simulating it?
My intuition is that the fastest classical algorithm for simulating some kind of noiseless quantum sampling process should scale roughly with the dimension of the Hilbert space: you would need to ...
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Has the possibility of there being a classical cryptography algorithm able to withstand quantum computing been proven?
Has it been proven, that a classical codec (encoder-decoder) (classical meaning one that doesn't require a quantum system for its operation) is possible, such that a quantum computer cannot crack it?
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Can error correction for a classical algorithm with bit flips be easier than for a general quantum circuit?
Assume one runs a purely classical algorithm on $n$ logical qubits on a physical device with some bit flip probability.
Can implementing error correction in this case be any easier than in the case of ...
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Are there problems that a classical computer can solve and a quantum computer can never solve?
Apologies if this is a silly question. But I've heard quantum computers can solve problems that classical computers can't. What about the converse, are there any problems that a classical computer can ...
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Why is sampling considered difficult on a classical computer but easy on a quantum computer? [closed]
It is my understanding that classical computers have a hard time sampling results from an output from a quantum circuit, but quantum computers find it very easy to do so. Why is this?
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What are the types of models of computation aside from the quantum query model?
It looks like in a lot of quantum algorithms, we use the quantum query model. I wanted to know what are the other types of models of computation, used in quantum computing as well as in classical ...
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What is the counting argument for the number of elementary operations required for a random function?
What is the counting argument for the following statement (classical)?
"A random function on n bits requires $e^{\Omega(n)}$ elementary operations."
It appears in the introduction of PRL 116,...
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Why can't quantum computation replace classical computation?
I am not a total novice of quantum computation (have read the first 6 chapters of Nielsen and Chuang, though not familiar with every part), but there are some fundamental questions that I don't know ...
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Are circuits with more than 1000 gates common?
I have seen circuits with 30 qubits and around 500 gates. Also circuits with 32 qubits and 6000 gates. Are circuits with more than 1000 gates common in quantum computing? Are there many quantum ...
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Can the difference between quantum and classical circuits be attributed to different paths in the Hilbert space?
One of the explanations I have encountered for why quantum computation can provide speed-up over the classical is a picture that in the Hilbert space much more paths are allowed quantum-mechanically ...
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When is a Quantum Computer Slower Than a Classical Computer?
Someone offhandedly mentioned to me that quantum computers are sometimes significantly (I guess they meant asymptotically) slower than classical computers.
Unfortunately, I didn't get any arguments ...
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Quantum computer speedups for classically efficient applications
I'm interested in learning about cases where a quantum computer could be used to perform tasks with only a constant (albeit large) factor of improvement in execution speed over classical computers. ...
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Using principle of deferred measurement to replace gates conditional on classical bits (c_if)
I am trying to implement the Iterative Phase Estimation algorithm on one of Qiskit's labs. I can do it for a 'nice' phase, such as 1/4 :
But if I want to implement the algo generally (as a subroutine ...
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What's the difference between open-source QRNG and Quantis Device?
qRNG is an open-source quantum random number generator written in python and Quantis RNG is a physical quantum random number generator. Both are capable of generating quantum random numbers, but how ...
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Shor vs Schnorr: A classical algorithm for breaking RSA? [duplicate]
I am not sure why I haven't heard much chatter about this paper by Dr. Claus Peter Schnorr where he claims to have come up with a classical algorithm to break the RSA protocol. The construction is ...
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Classical algorithm with complexity similar to Shor's discovered: Are there more efficient quantum algorithms than Shor's?
In the article Fast Factoring Integers by SVP Algorithms the author claims that he discovered classical algorithm for factoring integers in polynomial time. The Quantum Report mentioned here that it ...
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Are classical analogues of quantum computers using superposed waves possible? [duplicate]
The trick of quantum computing is to take the advantage of wave mechanics (superposition) and entanglement. This allows to perform parallel computations/manipulations with $2^n$ superposed waves for $...
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Generally speaking, are quantum speedups always due to parallelization of a given problem?
We know that quantum computers use the wave-like nature of quantum mechanics to perform interference. Sometimes we can use this interference to perform specific algorithms that will cause enough ...
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How do qubits in quantum computers work? [closed]
I was reading about quantum computers and qubits. While a classical bit can be either 0 or 1, a qubit can be 0 or 1 or both at the same time (can it be none too?). But how is this useful at all?
If it ...
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what matrix operations have better known time complexity on a quantum computer?
I'm exploring quantum computers for a semester project. I'm mainly interested in making faster matrix calculations than a regular computer.
I was wondering what arithmetic operations (irrespective of ...
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Aren't qubits just ternary?
Qubits have 3 states: 1, 0, and 1 and 0 at the same time. If a qubit can have 3 states, then how come they are seen as different from ternary computing, which also has 3 states?
Is it that the 3 ...
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If quantum computing always return random measurement (or uncertain measurement), why do we still need it?
I am very new to quantum computing and currently studying quantum computing on my own through various resources (Youtube Qiskit, Qiskit website, book).
As my mindset is still "locked" with ...
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No. of bits in 160 qubits computer [duplicate]
I read in a book that (https://hub.packtpub.com/quantum-expert-robert-sutor-explains-the-basics-of-quantum-computing/)
160 qubits (quantum bits) could hold $2^{160} \approx1.46\times 10^{48}$ bits ...
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Question on practical quantum computing programming code [duplicate]
Has anyone tried any quantum computing programming code that shows or demonstrates the advantage of a quantum computer over classical computers? Thanks a lot.
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Does 1 qubit correspond to 2 bits?
In a lot of presentation I always see people say that $n$ qbit are approximately $2^n$ classical bit.
Those talks where oriented for a broad audience, so they left out a lot of things.
Deep down I ...
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Is there an explanation for why, to search through an unstructured database, the average number of checks is $\frac{N}{2}$ in classical computation?
I have came across many books online that all explain that if $N$ is large enough, then the average number of checks in $N/2$ but is there a mathematical explanation or derivation for why this is true?...
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Papers on classical optimization in QAOA
Are there any papers on the classical optimization part of QAOA?
What is the most efficient method now?
And how is the classical optimization classified?
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What is the best way to use loop statements on a quantum computer?
I am interested in solving a time dependent linear partial differential equation of the form $Ax=b$ which, in classical computing, would amount to looping over solutions of $Ax=b$ where $b$ is updated ...
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Can hash functions speed up quantum simulation? (Generalizing May and Schlieper's idea)
Recently May and Schlieper have published a preprint (https://arxiv.org/abs/1905.10074) arguing that the modular exponential register in Shor's algorithms can be replaced with a universally hashed ...
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Can classical linear algebra solvers implement quantum algorithms with similar speed-ups?
A quantum algorithm begins with a register of qubits in an initial state, a unitary operator (the algorithm) manipulates the state of those qubits, and then the state of the qubits is read out (or at ...
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