Volume
LIPIcs, Volume 197
16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)
Event
TQC 2021, July 5-8, 2021, Virtual ConferenceEditor
Publication Details
- published at: 2021-06-22
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-198-6
- DBLP: db/conf/tqc/tqc2021
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Document
Complete Volume
LIPIcs, Volume 197, TQC 2021, Complete Volume
Abstract
LIPIcs, Volume 197, TQC 2021, Complete Volume
Cite as
16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 1-178, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@Proceedings{hsieh:LIPIcs.TQC.2021,
title = {{LIPIcs, Volume 197, TQC 2021, Complete Volume}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {1--178},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021},
URN = {urn:nbn:de:0030-drops-139940},
doi = {10.4230/LIPIcs.TQC.2021},
annote = {Keywords: LIPIcs, Volume 197, TQC 2021, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 0:i-0:xii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{hsieh:LIPIcs.TQC.2021.0,
author = {Hsieh, Min-Hsiu},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {0:i--0:xii},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.0},
URN = {urn:nbn:de:0030-drops-139958},
doi = {10.4230/LIPIcs.TQC.2021.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Quantum Time-Space Tradeoff for Finding Multiple Collision Pairs
Abstract
We study the problem of finding K collision pairs in a random function f : [N] → [N] by using a quantum computer. We prove that the number of queries to the function in the quantum random oracle model must increase significantly when the size of the available memory is limited. Namely, we demonstrate that any algorithm using S qubits of memory must perform a number T of queries that satisfies the tradeoff T³ S ≥ Ω(K³N). Classically, the same question has only been settled recently by Dinur [Dinur, 2020], who showed that the Parallel Collision Search algorithm of van Oorschot and Wiener [Oorschot and Wiener, 1999] achieves the optimal time-space tradeoff of T² S = Θ(K² N). Our result limits the extent to which quantum computing may decrease this tradeoff. Our method is based on a novel application of Zhandry’s recording query technique [Zhandry, 2019] for proving lower bounds in the exponentially small success probability regime. As a second application, we give a simpler proof of the time-space tradeoff T² S ≥ Ω(N³) for sorting N numbers on a quantum computer, which was first obtained by Klauck, Špalek and de Wolf [Klauck et al., 2007].
Cite as
Yassine Hamoudi and Frédéric Magniez. Quantum Time-Space Tradeoff for Finding Multiple Collision Pairs. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 1:1-1:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{hamoudi_et_al:LIPIcs.TQC.2021.1,
author = {Hamoudi, Yassine and Magniez, Fr\'{e}d\'{e}ric},
title = {{Quantum Time-Space Tradeoff for Finding Multiple Collision Pairs}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {1:1--1:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.1},
URN = {urn:nbn:de:0030-drops-139961},
doi = {10.4230/LIPIcs.TQC.2021.1},
annote = {Keywords: Quantum computing, query complexity, lower bound, time-space tradeoff}
}
Document
Quantum Pseudorandomness and Classical Complexity
Abstract
We construct a quantum oracle relative to which BQP = QMA but cryptographic pseudorandom quantum states and pseudorandom unitary transformations exist, a counterintuitive result in light of the fact that pseudorandom states can be "broken" by quantum Merlin-Arthur adversaries. We explain how this nuance arises as the result of a distinction between algorithms that operate on quantum and classical inputs. On the other hand, we show that some computational complexity assumption is needed to construct pseudorandom states, by proving that pseudorandom states do not exist if BQP = PP. We discuss implications of these results for cryptography, complexity theory, and quantum tomography.
Cite as
William Kretschmer. Quantum Pseudorandomness and Classical Complexity. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 2:1-2:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{kretschmer:LIPIcs.TQC.2021.2,
author = {Kretschmer, William},
title = {{Quantum Pseudorandomness and Classical Complexity}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {2:1--2:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.2},
URN = {urn:nbn:de:0030-drops-139975},
doi = {10.4230/LIPIcs.TQC.2021.2},
annote = {Keywords: pseudorandom quantum states, quantum Merlin-Arthur}
}
Document
Sample Efficient Algorithms for Learning Quantum Channels in PAC Model and the Approximate State Discrimination Problem
Abstract
The probably approximately correct (PAC) model [Leslie G. Valiant, 1984] is a well studied model in classical learning theory. Here, we generalize the PAC model from concepts of Boolean functions to quantum channels, introducing PAC model for learning quantum channels, and give two sample efficient algorithms that are analogous to the classical "Occam’s razor" result [Blumer et al., 1987]. The classical Occam’s razor algorithm is done trivially by excluding any concepts not compatible with the input-output pairs one gets, but such an approach is not immediately possible with a concept class of quantum channels, because the outputs are unknown quantum states from the quantum channel.
To study the quantum state learning problem associated with PAC learning quantum channels, we focus on the special case where the channels all have constant output. In this special case, learning the channels reduce to a problem of learning quantum states that is similar to the well known quantum state discrimination problem [Joonwoo Bae and Leong-Chuan Kwek, 2017], but with the extra twist that we allow ε-trace-distance-error in the output. We call this problem Approximate State Discrimination, which we believe is a natural problem that is of independent interest.
We give two algorithms for learning quantum channels in PAC model. The first algorithm has sample complexity
O((log|C| + log(1/ δ))/(ε²)),
but only works when the outputs are pure states, where C is the concept class, ε is the error of the output, and δ is the probability of failure of the algorithm. The second algorithm has sample complexity
O((log³|C|(log|C|+log(1/ δ)))/(ε²)),
and work for mixed state outputs. Some implications of our results are that we can PAC-learn a polynomial sized quantum circuit in polynomial samples, and approximate state discrimination can be solved in polynomial samples even when the size of the input set is exponential in the number of qubits, exponentially better than a naive state tomography.
Cite as
Kai-Min Chung and Han-Hsuan Lin. Sample Efficient Algorithms for Learning Quantum Channels in PAC Model and the Approximate State Discrimination Problem. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 3:1-3:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{chung_et_al:LIPIcs.TQC.2021.3,
author = {Chung, Kai-Min and Lin, Han-Hsuan},
title = {{Sample Efficient Algorithms for Learning Quantum Channels in PAC Model and the Approximate State Discrimination Problem}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {3:1--3:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.3},
URN = {urn:nbn:de:0030-drops-139984},
doi = {10.4230/LIPIcs.TQC.2021.3},
annote = {Keywords: PAC learning, Quantum PAC learning, Sample Complexity, Approximate State Discrimination, Quantum information}
}
Document
StoqMA Meets Distribution Testing
Abstract
StoqMA captures the computational hardness of approximating the ground energy of local Hamiltonians that do not suffer the so-called sign problem. We provide a novel connection between StoqMA and distribution testing via reversible circuits. First, we prove that easy-witness StoqMA (viz. eStoqMA, a sub-class of StoqMA) is contained in MA. Easy witness is a generalization of a subset state such that the associated set’s membership can be efficiently verifiable, and all non-zero coordinates are not necessarily uniform. This sub-class eStoqMA contains StoqMA with perfect completeness (StoqMA₁), which further signifies a simplified proof for StoqMA₁ ⊆ MA [Bravyi et al., 2006; Bravyi and Terhal, 2010]. Second, by showing distinguishing reversible circuits with ancillary random bits is StoqMA-complete (as a comparison, distinguishing quantum circuits is QMA-complete [Janzing et al., 2005]), we construct soundness error reduction of StoqMA. Additionally, we show that both variants of StoqMA that without any ancillary random bit and with perfect soundness are contained in NP. Our results make a step towards collapsing the hierarchy MA ⊆ StoqMA ⊆ SBP [Bravyi et al., 2006], in which all classes are contained in AM and collapse to NP under derandomization assumptions.
Cite as
Yupan Liu. StoqMA Meets Distribution Testing. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 4:1-4:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{liu:LIPIcs.TQC.2021.4,
author = {Liu, Yupan},
title = {{StoqMA Meets Distribution Testing}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {4:1--4:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.4},
URN = {urn:nbn:de:0030-drops-139995},
doi = {10.4230/LIPIcs.TQC.2021.4},
annote = {Keywords: StoqMA, distribution testing, error reduction, reversible circuits}
}
Document
Fault-Tolerant Syndrome Extraction and Cat State Preparation with Fewer Qubits
Abstract
We reduce the extra qubits needed for two fault-tolerant quantum computing protocols: error correction, specifically syndrome bit measurement, and cat state preparation. For fault-tolerant syndrome extraction, we show an exponential reduction in qubit overhead over the previous best protocol. For a weight-w stabilizer, we demonstrate that stabilizer measurement tolerating one fault (distance-three) needs at most ⌈ log₂ w ⌉ + 1 ancillas. If qubits reset quickly, four ancillas suffice. We also study the preparation of cat states, simple yet versatile entangled states. We prove that the overhead needed for distance-three fault tolerance is only logarithmic in the cat state size. These results could be useful both for near-term experiments with a few qubits, and for the general study of the asymptotic resource requirements of syndrome measurement and state preparation.
For 'a' measured flag bits, there are 2^a possible flag patterns that can identify faults. Hence our results come from solving a combinatorial problem: the construction of maximal-length paths in the a-dimensional hypercube, corresponding to maximal-weight stabilizers or maximal-weight cat states.
Cite as
Prithviraj Prabhu and Ben W. Reichardt. Fault-Tolerant Syndrome Extraction and Cat State Preparation with Fewer Qubits. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 5:1-5:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{prabhu_et_al:LIPIcs.TQC.2021.5,
author = {Prabhu, Prithviraj and Reichardt, Ben W.},
title = {{Fault-Tolerant Syndrome Extraction and Cat State Preparation with Fewer Qubits}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {5:1--5:13},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.5},
URN = {urn:nbn:de:0030-drops-140001},
doi = {10.4230/LIPIcs.TQC.2021.5},
annote = {Keywords: Quantum error correction, fault tolerance, quantum state preparation, combinatorics}
}
Document
A Note About Claw Function with a Small Range
Abstract
In the claw detection problem we are given two functions f:D → R and g:D → R (|D| = n, |R| = k), and we have to determine if there is exist x,y ∈ D such that f(x) = g(y). We show that the quantum query complexity of this problem is between Ω(n^{1/2}k^{1/6}) and O(n^{1/2+ε}k^{1/4}) when 2 ≤ k < n.
Cite as
Andris Ambainis, Kaspars Balodis, and Jānis Iraids. A Note About Claw Function with a Small Range. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 6:1-6:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{ambainis_et_al:LIPIcs.TQC.2021.6,
author = {Ambainis, Andris and Balodis, Kaspars and Iraids, J\={a}nis},
title = {{A Note About Claw Function with a Small Range}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {6:1--6:5},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.6},
URN = {urn:nbn:de:0030-drops-140013},
doi = {10.4230/LIPIcs.TQC.2021.6},
annote = {Keywords: collision, claw, quantum query complexity}
}
Document
Fast and Robust Quantum State Tomography from Few Basis Measurements
Abstract
Quantum state tomography is a powerful but resource-intensive, general solution for numerous quantum information processing tasks. This motivates the design of robust tomography procedures that use relevant resources as sparingly as possible. Important cost factors include the number of state copies and measurement settings, as well as classical postprocessing time and memory. In this work, we present and analyze an online tomography algorithm designed to optimize all the aforementioned resources at the cost of a worse dependence on accuracy. The protocol is the first to give provably optimal performance in terms of rank and dimension for state copies, measurement settings and memory. Classical runtime is also reduced substantially and numerical experiments demonstrate a favorable comparison with other state-of-the-art techniques. Further improvements are possible by executing the algorithm on a quantum computer, giving a quantum speedup for quantum state tomography.
Cite as
Daniel Stilck França, Fernando G.S L. Brandão, and Richard Kueng. Fast and Robust Quantum State Tomography from Few Basis Measurements. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 7:1-7:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{franca_et_al:LIPIcs.TQC.2021.7,
author = {Fran\c{c}a, Daniel Stilck and Brand\~{a}o, Fernando G.S L. and Kueng, Richard},
title = {{Fast and Robust Quantum State Tomography from Few Basis Measurements}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {7:1--7:13},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.7},
URN = {urn:nbn:de:0030-drops-140023},
doi = {10.4230/LIPIcs.TQC.2021.7},
annote = {Keywords: quantum tomography, low-rank tomography, Gibbs states, random measurements}
}
Document
Pauli Error Estimation via Population Recovery
Abstract
Motivated by estimation of quantum noise models, we study the problem of learning a Pauli channel, or more generally the Pauli error rates of an arbitrary channel. By employing a novel reduction to the "Population Recovery" problem, we give an extremely simple algorithm that learns the Pauli error rates of an n-qubit channel to precision ε in 𝓁_∞ using just O(1/ε²) log(n/ε) applications of the channel. This is optimal up to the logarithmic factors. Our algorithm uses only unentangled state preparation and measurements, and the post-measurement classical runtime is just an O(1/ε) factor larger than the measurement data size. It is also impervious to a limited model of measurement noise where heralded measurement failures occur independently with probability ≤ 1/4.
We then consider the case where the noise channel is close to the identity, meaning that the no-error outcome occurs with probability 1-η. In the regime of small η we extend our algorithm to achieve multiplicative precision 1 ± ε (i.e., additive precision εη) using just O(1/(ε²η)) log(n/ε) applications of the channel.
Cite as
Steven T. Flammia and Ryan O'Donnell. Pauli Error Estimation via Population Recovery. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 8:1-8:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{flammia_et_al:LIPIcs.TQC.2021.8,
author = {Flammia, Steven T. and O'Donnell, Ryan},
title = {{Pauli Error Estimation via Population Recovery}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {8:1--8:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.8},
URN = {urn:nbn:de:0030-drops-140034},
doi = {10.4230/LIPIcs.TQC.2021.8},
annote = {Keywords: Pauli channels, population recovery, Goldreich-Levin, sparse recovery, quantum channel tomography}
}
Document
Quantum Probability Oracles & Multidimensional Amplitude Estimation
Abstract
We give a multidimensional version of amplitude estimation. Let p be an n-dimensional probability distribution which can be sampled from using a quantum circuit U_p. We show that all coordinates of p can be estimated up to error ε per coordinate using Õ(1/(ε)) applications of U_p and its inverse. This generalizes the normal amplitude estimation algorithm, which solves the problem for n = 2. Our results also imply a Õ(n/ε) query algorithm for 𝓁₁-norm (the total variation distance) estimation and a Õ(√n/ε) query algorithm for 𝓁₂-norm. We also show that these results are optimal up to logarithmic factors.
Cite as
Joran van Apeldoorn. Quantum Probability Oracles & Multidimensional Amplitude Estimation. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 9:1-9:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{vanapeldoorn:LIPIcs.TQC.2021.9,
author = {van Apeldoorn, Joran},
title = {{Quantum Probability Oracles \& Multidimensional Amplitude Estimation}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {9:1--9:11},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.9},
URN = {urn:nbn:de:0030-drops-140046},
doi = {10.4230/LIPIcs.TQC.2021.9},
annote = {Keywords: quantum algorithms, amplitude estimation, monte carlo}
}
Document
Quantum Logarithmic Space and Post-Selection
Abstract
Post-selection, the power of discarding all runs of a computation in which an undesirable event occurs, is an influential concept introduced to the field of quantum complexity theory by Aaronson (Proceedings of the Royal Society A, 2005). In the present paper, we initiate the study of post-selection for space-bounded quantum complexity classes. Our main result shows the identity PostBQL = PL, i.e., the class of problems that can be solved by a bounded-error (polynomial-time) logarithmic-space quantum algorithm with post-selection (PostBQL) is equal to the class of problems that can be solved by unbounded-error logarithmic-space classical algorithms (PL). This result gives a space-bounded version of the well-known result PostBQP = PP proved by Aaronson for polynomial-time quantum computation. As a by-product, we also show that PL coincides with the class of problems that can be solved by bounded-error logarithmic-space quantum algorithms that have no time bound.
Cite as
François Le Gall, Harumichi Nishimura, and Abuzer Yakaryılmaz. Quantum Logarithmic Space and Post-Selection. In 16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 197, pp. 10:1-10:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
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@InProceedings{legall_et_al:LIPIcs.TQC.2021.10,
author = {Le Gall, Fran\c{c}ois and Nishimura, Harumichi and Yakary{\i}lmaz, Abuzer},
title = {{Quantum Logarithmic Space and Post-Selection}},
booktitle = {16th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2021)},
pages = {10:1--10:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-198-6},
ISSN = {1868-8969},
year = {2021},
volume = {197},
editor = {Hsieh, Min-Hsiu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2021.10},
URN = {urn:nbn:de:0030-drops-140054},
doi = {10.4230/LIPIcs.TQC.2021.10},
annote = {Keywords: computational complexity, space-bounded quantum computation, post-selection}
}