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Quantum Complexity Theory

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lightbulbAbout this topic
Quantum Complexity Theory is a subfield of theoretical computer science that studies the resources required to solve computational problems using quantum computers. It explores the classification of problems based on their complexity in the quantum realm, comparing quantum algorithms' efficiency to classical counterparts and investigating the implications for computational limits and capabilities.
lightbulbAbout this topic
Quantum Complexity Theory is a subfield of theoretical computer science that studies the resources required to solve computational problems using quantum computers. It explores the classification of problems based on their complexity in the quantum realm, comparing quantum algorithms' efficiency to classical counterparts and investigating the implications for computational limits and capabilities.

Key research themes

1. How does the interplay between quantum physical principles and information geometry shape the foundations and complexity of quantum computation?

This theme explores foundational approaches to quantum complexity and quantum theory rooted in physical principles, geometric structures, and information-theoretic frameworks. It focuses on how the intrinsic geometric and statistical properties of quantum systems inform complexity measures of quantum processes, quantum states, and algorithmic tasks, providing a mathematically rigorous underpinning that connects quantum theory’s epistemic interpretation, resource theories, and computational complexity.

Key finding: This paper develops a unified axiomatic framework for resource-dependent complexity measures of general quantum channels using noncommutative geometry tools. It introduces Lipschitz complexity, a geometric measure grounded in... Read more
Key finding: By restricting Gacs’s quantum algorithmic complexity to ergodic classical dynamical systems, the equality between algorithmic (Kolmogorov) complexity rate and Shannon entropy rate is retrieved (Brudno’s theorem). Further, via... Read more
Key finding: This paper proposes a foundation of quantum theory based on 'theoretical variables' associated with observers, distinguishing accessible and inaccessible variables, and constructs the Hilbert space formalism using group... Read more
Key finding: This foundational work explicitly formulates the Church–Turing principle as a physical postulate stating that every finitely realizable physical system can be perfectly simulated by a universal computing device operating by... Read more
Key finding: This paper provides an epistemic approach linking conceptual variables used in quantum mechanics to decision variables, developing a simple measurement model foundationally deriving quantum measurement axioms. It shows that... Read more

2. What are the computational advantages and challenges of quantum algorithms in relation to classical machine learning and communication complexity?

This theme investigates quantum computational supremacy, the power of quantum algorithms in machine learning applications, and the relationship between classical and quantum communication complexity measures. It encompasses algorithmic design, resource requirements, and the quantification of quantum speed-ups over classical counterparts. It also considers practical and theoretical bottlenecks in discovering and implementing quantum algorithms, including hybrid quantum-classical models and the complexity involved in realizing quantum states as inputs and outputs of algorithms.

Key finding: The paper performs a comprehensive complexity analysis of all stages involved in implementing quantum algorithms, including quantum input state preparation and measurement readout processes, which are often neglected. It... Read more
Key finding: This work advances understanding of the gap between classical and quantum one-way communication complexities, presenting new upper bounds on classical communication complexity as a function of quantum one-way communication... Read more
Key finding: Providing a research panorama accessible to computer scientists, this review synthesizes quantum machine learning (QML) approaches demonstrating quantum speed-ups for key algorithmic primitives (e.g., Grover’s and Shor’s... Read more
Key finding: The paper proposes MAQA, a universal and efficient quantum framework amenable to realizing a diverse family of classical supervised learning models—including ensemble methods and neural networks—by quantum aggregation of... Read more

3. How do quantum structures and logics enable new models for computation, semantics, and interactive information processing beyond classical paradigms?

This research direction focuses on the application of quantum mathematical structures—such as Hilbert spaces, quantum logic, and contextuality—to domains beyond quantum physics including computer science areas like semantics, information retrieval, and probabilistic programming. It investigates how fundamentally non-classical features of quantum theory (e.g., superposition, interference, contextuality) inspire novel computational and data representation frameworks that potentially overcome classical limitations, allowing for richer conceptual modeling, multi-modal data fusion, and flexible interactive systems.

Key finding: This comprehensive collection of articles showcases how quantum theoretical structures—such as complex Hilbert spaces and quantum probability models—can be harnessed to model semantic spaces, multi-modal information fusion,... Read more
Key finding: Introducing a formal language for types of higher-order quantum transformations, this work classifies maps from quantum combs to combs, elucidating the hierarchy of quantum operations beyond standard quantum circuits,... Read more
Key finding: Though serving as a positioning editorial, this preface emphasizes the promise of quantum computing’s intrinsic parallelism, superposition, and interference to tackle traditionally hard computational problems in cryptography... Read more

All papers in Quantum Complexity Theory

Este trabajo presenta una demostración rigurosa de la monotonicidad de entropías estabilizadoras S_α(ρ)= (1/(1-α))log(Tr(ρ^α)) para parámetros α ≥ 2 bajo transformaciones completamente positivas quepreservan la traza (CPTP) y mantienen la... more
This paper presents Universal Displacement Theory (UDT), a theoretical framework proposing that fundamental forces emerge from substrate displacement mechanics rather than field-based interactions. The theory suggests that particle... more
G-Theory primary contributions to science... ( You may wish to just copy and paste the content of the paper to your preferred ai. And request an evaluation. Cheers!) This paper proposes a radical new **Unified Field Theory,... more
The classification and relationships between computational complexity classes represent one of the most fundamental open problems in theoretical computer science and mathematics. While significant progress has been made in understanding... more
Kolmogorov complexity is a measure of the information contained in a binary string. We investigate here the notion of quantum Kolmogorov complexity, a measure of the information required to describe a quantum state. We show that for any... more
Kolmogorov complexity is a measure of the information contained in a binary string. We investigate here the notion of quantum Kolmogorov complexity, a measure of the information required to describe a quantum state. We show that for any... more
We give a definition for the Kolmogorov complexity of a pure quantum state. In classical information theory, the algorithmic complexity of a string is a measure of the information needed by a universal machine to reproduce the string... more
We define the algorithmic complexity of a quantum state relative to a given precision parameter, and give upper bounds for various examples of states. We also establish a connection between the entanglement of a quantum state and its... more
We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP. • BQP is low for PP, i.e.,... more
At the threshold where light surrenders to gravity's embrace lies a mathematical structure of profound elegance. This paper unveils a formalisation of black hole physics through the crystalline lens of information geometry, where the... more
We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP. • BQP is low for PP, i.e.,... more
Computing the ground-state energy of interacting electron (fermion) problems has recently been shown to be hard for QMA, a quantum analogue of the complexity class NP. Fermionic problems are usually hard, a phenomenon widely attributed to... more
We describe Kitaev's result from 1999, in which he defines the complexity class QMA, the quantum analog of the class NP, and shows that a natural extension of 3−SAT, namely local Hamiltonians, is QMA complete. The result builds upon the... more
Quantum complexity theory is concerned with the amount of elementary quantum resources needed to build a quantum system or a quantum operation. The fundamental question in quantum complexity is to define and quantify suitable complexity... more
State transformation problems such as compressing quantum information or breaking quantum commitments are fundamental quantum tasks. However, their computational difficulty cannot easily be characterized using traditional complexity... more
Inspired by random walk on graphs, diffusion map (DM) is a class of unsupervised machine learning that offers automatic identification of low-dimensional data structure hidden in a highdimensional dataset. In recent years, among its many... more
The creation complexity of a quantum state is the minimum number of elementary gates required to create it from a basic initial state. The creation complexity of quantum states is closely related to the complexity of quantum circuits,... more
In the past few years there has been a tumultuous activity aimed at introducing novel conceptual schemes for quantum computing. The approach proposed in (Marzuoli A and Rasetti M 2002, 2005a) relies on the (re)coupling theory of SU(2)... more
We analyze the connections between the mathematical theory of knots and quantum physics by addressing a number of algorithmic questions related to both knots and braid groups. Knots can be distinguished by means of 'knot invariants',... more
In this article we introduce a new complexity class called PQMA log (2). Informally, this is the class of languages for which membership has a logarithmic-size quantum proof with perfect completeness and soundness which is polynomially... more
In this article we introduce a new complexity class called PQMA log (2). Informally, this is the class of languages for which membership has a logarithmic-size quantum proof with perfect completeness and soundness which is polynomially... more
In this review article, we are interested in the detailed analysis of complexity aspects of both time and space that arises from the implementation of a quantum algorithm on a quantum based hardware. In particular, some steps of the... more
In this work, we are interested in the detailed analysis of complexity aspects of both time and space that arises from the implementation of a quantum algorithm on a quantum based hardware. In particular, some steps of the implementation,... more
To which extent the whole of a system cannot be reduced into the sum of its parts? Apart from complexity theory, this question stands on the core of composite quantum states structure, given the intrinsic structural properties of Hilbert... more
We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP. • BQP is low for PP, i.e.,... more
In this note we show that all languages in NP have very short (logarithmic size) quantum proofs which can be verified provided that two unentangled copies are given. We thus introduce a new complexity class QMA log (2) and show that NP ⊆... more
In this note we show that all languages in NP have very short (logarithmic size) quantum proofs which can be verified provided that two unentangled copies are given. We thus introduce a new complexity class QMA log (2) and show that NP ⊆... more
In this paper we present the computational model underlying the one-way quantum computer which we introduced recently [Phys. Rev. Lett. {\bf{86}}, 5188 (2001)]. The one-way quantum computer has the property that any quantum logic network... more
We define the algorithmic complexity of a quantum state relative to a given precision parameter, and give upper bounds for various examples of states. We also establish a connection between the entanglement of a quantum state and its... more
We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP. • BQP is low for PP, i.e.,... more
Motivated by the result that an 'approximate' evaluation of the Jones polynomial of a braid at a 5 th root of unity can be used to simulate the quantum part of any algorithm in the quantum complexity class BQP, and results relating BQP to... more
This handout was created in the context of a talk we gave at the \Graduate Seminar on Topics in Quantum Computation" by Prof. Nitin Saxena at the University of Bonn in the Summer Semester 2011. It is heavily based on the lecture... more
In the past few years there has been a tumultuous activity aimed at introducing novel conceptual schemes for quantum computing. The approach proposed in (Marzuoli A and Rasetti M 2002, 2005a) relies on the (re)coupling theory of SU(2)... more
Previouslywe noted in numerical calculations that a certain unitary ninej coefficient U9j =((jj) 2j (jj) 2j | (jj) 2j (jj) (2j−2)) I decreases with increasing j and for small I the decrease is of the form C j m e −αj. The exponential... more
In the past few years there has been a tumultuous activity aimed at introducing novel conceptual schemes for quantum computing. The approach proposed in (Marzuoli A and Rasetti M 2002, 2005a) relies on the (re)coupling theory of SU(2)... more
In the past few years there has been a tumultuous activity aimed at introducing novel conceptual schemes for quantum computing. The approach proposed in Rasetti M 2002, 2005a) relies on the (re)coupling theory of SU(2) angular momenta and... more
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