Questions tagged [classical-computing]

For questions about the relation between quantum computing and classical computing, such as their relative performance.

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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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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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What exactly makes quantum computers faster than classical computers?

What feature of a quantum algorithm makes it better than its classical counterpart? Are quantum computers faster than classical ones in all respects?
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Does a quantum computer have a clock signal and if yes how big is it?

I think there can't be a computer running software without having a clock signal. A fast classical computer has a clock rate between 4 to 5 GHz. If quantum computers are so much faster they must have ...
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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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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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Will Moore's Law be no longer effective once quantum computers are created? [duplicate]

Moore's law states that computer power doubles in every 18 months (more formally: "the number of transistors in a dense integrated circuit doubles about every two years."). Statistics suggest that ...
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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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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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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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Can a quantum computer simulate a normal computer?

Similar to the question Could a Turing Machine simulate a quantum computer?: given a 'classical' algorithm, is it always possible to formulate an equivalent algorithm which can be performed on a ...
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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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STO-3G Basis Set

Can someone please explain why STO-3G is considered to be a good basis set for quantum computing, while it does not help in classical computing? I would also be very grateful for any references to ...
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Is quantum computing just pie in the sky?

I have a computer science degree. I work in IT, and have done so for many years. In that period "classical" computers have advanced by leaps and bounds. I now have a terabyte disk drive in my bedroom ...
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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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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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Does quantum computing already possess the level of abstraction to be explicable even without knowledge of physics?

Currently, quantum computer science (in contrast to classical computer science) can mostly only be understood if one has a good inside knowledge of physics, or more precisely quantum physics. Only ...
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Quantum circuits explain algorithms, why didn't classical circuits?

When explaining a quantum algorithm, many revert to 'circuit-speak' by drawing a diagram of how qubits split off into transformations and measurements, however, rarely if not never would someone ...
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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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Is it right to think of superposition as just angle?

Based on my current understanding, a qubit is represented as a vector $(a, b)$ which satisfy $a^2 + b^2 = 1$. Classical bit one can be represented as $(0, 1)$ and bit zero can be represented as $(1, ...
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Are we certain that quantum computers are more efficient than classical computers can be built?

I mean are we certain that they will be able to provide us a huge improvements (in some tasks) compared to clasical computers?
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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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Is it possible to “calculate” the absolute value of a permanent using Boson Sampling?

In boson sampling, if we start with 1 photon in each of the first $M$ modes of an interferometer, the probability of detecting 1 photon in each output mode is: $|\textrm{Perm}(A)|^2$, where the ...
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Why is it harder to build quantum computers than classical computers?

Is it because we don't know exactly how to create quantum computers (and how they must work), or do we know how to create it in theory, but don't have the tools to actually execute it in practice? Is ...
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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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Is it possible to convert classical algorithms to quantum ones?

I am new in this field and I am considering to do research for my engineering degree. First, I would like to have an opinion from more experienced people. Do you think it is possible to convert ...
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What are some general concepts of how a classical computer would interface with a quantum computer?

Very general question so I'm not looking for an exact answer. I just want a basic description of certain ways it can be done and then if possible the names of those ways, so that I can look them up ...
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Is quantum cryptography safer than classical cryptography?

Quantum computing allows us to encrypt information in a different way compared to what we use today, but quantum computers are much more powerful than today's computers. So if we manage to build ...
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Compiling a classical function to a quantum circuit in practice

It can be shown that any classical function $f$ can be implemented by a quantum circuit $Q_f$, so that $$ \sum_{x}|x,0^k\rangle \xrightarrow{\mathit{Q_f}} \sum_{x}|x,f(x)\rangle $$ where $f$ has $k$ ...
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How does a classical computer simulate nonclassical correlations?

This may be a dumb question, if so please forgive me, it is late at night. I have learned that a classical computer can simulate a quantum computer in exponential time and space, but classical ...
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References on quantum arithmetic circuit complexity

In classical computing, arithmetic circuit complexity is apparently a big topic. But I couldn't find much about the complexity of quantum arithmetic circuits. Almost all references like arXiv:1805....
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Classical computations from restricted quantum gates

The CNOT gate together with phase shift gates for all possible angles are not universal for quantum computing. Are they also not universal for classical (reversible) computing? Is it possible to ...
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Simplest algorithm for intuitively demonstrating quantum speed-up?

What's the simplest algorithm (like Deutsch's algorithm and Grover's Algorithm) for intuitively demonstrating quantum speed-up? And can this algorithm be explained intuitively? Ideally this would be ...
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Does a classical computer really require $2^n$ complex numbers to represent the state of $n$ qubit quantum computer?

One often reads that the key reason why classical computers (probabilistic or deterministic) are unable to simulate quantum algorithms such as Simon's or Shor's efficiently is that a classical ...
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How much memory is required to simulate a 48-qubit circuit?

This CDMTCS Report 514, 2017 entitled "The Road to Quantum Computational Supremacy" states (in Section 6) that the amount of memory needed to simulate random quantum circuits on classical computers ...
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Can I learn Quantum Programming and then go back to learn the Mathematics / Physics behind it later?

Learning from the ground up (while great) is an overdose of the mathematics behind quantum computing and is taking way too long to grasp. I have a Computer Science / Programming background. I am ...
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CPTP, Kraus representation and classical registers

What is the best mathematical representation of a quantum system that has some classical registers and some quantum registers? I'm asking because I'm considering any "physical" process $\pi()$ that ...
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What does the $\sqrt{NOT}$ gate have to do with irreversibility?

In his essay "Why now is the right time to study quantum computing" Aram Harrow writes, after describing the action of the $\sqrt{NOT}$ gate, that: However, if we apply $\sqrt{NOT}$ a second time ...
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Will quantum computers pass the Turing test? [closed]

Will quantum computers be able to pass the Turing test sooner than classical computers?
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Is there anything that can be programmed on a classical computer but not on a quantum computer?

Would we need to create new algorithms that only work on quantum computers or would be simply edit codes in languages such as C++ to involve the new primitives from quantum computing? Are there ...
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Does the massive parallelization in Quantum computing imply parallelization of input (as opposed to Turing machine)?

Being a newbie in this field, I'm trying to understand what types of real-life workloads are suitable for migrating to Quantum computers. Intuitively, it seems to me that if a Quantum computer ingests ...
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What concepts from classical computing are vital for quantum programmers?

Many scientific programmers get by fine without having a computer science background, i.e. they don't need to know the machinery behind the prevailing paradigm of 0's and 1's (bits), let alone basic ...
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Are quantum gates analogous to ASSPs in classical computing?

After reading some with regard to the quantum computing gates and the comparison to classic gates it seems that the quantum computer, at least for the time being, is not viewed as a programmable ...
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Are quantum computers just a variant on Analog computers of the 50's & 60's that many have never seen nor used?

In the recent Question "Is Quantum Computing just Pie in the Sky" there are many responses regarding the improvements in quantum capabilities, however all are focussed on the current 'digital' ...