The Programme Committee of TQC 2024 selected 92 out of 460 submissions for a contributed talk (20% acceptance rate).
You may find the contributed talks here.
The list of accepted posters will be published on the 2nd of May, after the poster notification date. The conference schedule will be published in July.
Note on the list: The talks are listed in alphabetical order of title. Later they will be listed by day of presentation. The topic tags were self-selected by the authors upon submission, given the options provided by the PC chairs.
1.
Kuo-Chin Chen, Simon Apers, Min-Hsiu Hsieh
(Quantum) complexity of testing signed graph clusterability Talk
2024.
Abstract | Tags: Other, Proceedings, Quantum algorithms
@Talk{T24_234,
title = {(Quantum) complexity of testing signed graph clusterability},
author = {Kuo-Chin Chen and Simon Apers and Min-Hsiu Hsieh},
year = {2024},
date = {2024-01-01},
abstract = {This study examines clusterability testing for a signed graph in the bounded-degree model. Our contributions are two-fold. First, we provide a quantum algorithm with query complexity $tildeO(N^1/3)$ for testing clusterability, which yields a polynomial speedup over the best classical clusterability tester known [Florian Adriaens and Simon Apers. Testing cluster properties of signed graphs.]. Second, we prove an $tildeØmega(sqrtN)$ classical query lower bound for testing clusterability, which nearly matches the upper bound from citeadriaens2021testing. This settles the classical query complexity of clusterability testing, and it shows that our quantum algorithm has an advantage over any classical algorithm.},
keywords = {Other, Proceedings, Quantum algorithms},
pubstate = {published},
tppubtype = {Talk}
}
This study examines clusterability testing for a signed graph in the bounded-degree model. Our contributions are two-fold. First, we provide a quantum algorithm with query complexity $tildeO(N^1/3)$ for testing clusterability, which yields a polynomial speedup over the best classical clusterability tester known [Florian Adriaens and Simon Apers. Testing cluster properties of signed graphs.]. Second, we prove an $tildeØmega(sqrtN)$ classical query lower bound for testing clusterability, which nearly matches the upper bound from citeadriaens2021testing. This settles the classical query complexity of clusterability testing, and it shows that our quantum algorithm has an advantage over any classical algorithm.
2.
Aleksandrs Belovs
A Direct Reduction from the Polynomial to the Adversary Method Talk
2024.
Abstract | Tags: Proceedings, Quantum algorithms, Quantum complexity theory
@Talk{T24_288,
title = {A Direct Reduction from the Polynomial to the Adversary Method},
author = {Aleksandrs Belovs},
year = {2024},
date = {2024-01-01},
abstract = {The polynomial and the adversary methods are the two main tools for proving lower bounds on query complexity of quantum algorithms. Both methods have found a large number of applications, some problems more suitable for one method, some for the other. It is known though that the adversary method, in its general negative-weighted version, is tight for bounded-error quantum algorithms, whereas the polynomial method is not. By the tightness of the former, for any polynomial lower bound, there ought to exist a corresponding adversary lower bound. However, direct reduction was not known. In this paper, we give a simple and direct reduction from the polynomial method (in the form of a dual polynomial) to the adversary method. This shows that any lower bound in the form of a dual polynomial is actually an adversary lower bound of a specific form.},
keywords = {Proceedings, Quantum algorithms, Quantum complexity theory},
pubstate = {published},
tppubtype = {Talk}
}
The polynomial and the adversary methods are the two main tools for proving lower bounds on query complexity of quantum algorithms. Both methods have found a large number of applications, some problems more suitable for one method, some for the other. It is known though that the adversary method, in its general negative-weighted version, is tight for bounded-error quantum algorithms, whereas the polynomial method is not. By the tightness of the former, for any polynomial lower bound, there ought to exist a corresponding adversary lower bound. However, direct reduction was not known. In this paper, we give a simple and direct reduction from the polynomial method (in the form of a dual polynomial) to the adversary method. This shows that any lower bound in the form of a dual polynomial is actually an adversary lower bound of a specific form.
3.
Wenhao He, Tongyang Li, Xiantao Li, Zecheng Li, Chunhao Wang, Ke Wang
Efficient Optimal Control of Open Quantum Systems Talk
2024.
Abstract | Tags: Proceedings, Quantum algorithms, Quantum information theory, Simulation of quantum systems
@Talk{T24_423,
title = {Efficient Optimal Control of Open Quantum Systems},
author = {Wenhao He and Tongyang Li and Xiantao Li and Zecheng Li and Chunhao Wang and Ke Wang},
year = {2024},
date = {2024-01-01},
abstract = {The optimal control problem for open quantum systems can be formulated as a time- dependent Lindbladian that is parameterized by a number of time-dependent control variables. Given an observable and an initial state, the goal is to tune the control variables so that the expected value of some observable with respect to the final state is maximized. In this paper, we present algorithms for solving this optimal control problem efficiently, i.e., having a poly-logarithmic dependency on the system dimension, which is exponentially faster than best-known classical algorithms. Our algorithms are hybrid, consisting of both quantum and classical components. The quantum procedure simulates time-dependent Lindblad evolution that drives the initial state to the final state, and it also provides access to the gradients of the objective function via quantum gradient estimation. The classical procedure uses the gradient information to update the control variables. At the technical level, we provide the first (to the best of our knowledge) simulation al- gorithm for time-dependent Lindbladians with an ℓ1-norm dependence. As an alternative, we also present a simulation algorithm in the interaction picture to improve the algorithm for the cases where the time-independent component of a Lindbladian dominates the time-dependent part. On the classical side, we heavily adapt the state-of-the-art classical optimization analysis to interface with the quantum part of our algorithms. Both the quantum simulation techniques and the classical optimization analyses might be of independent interest},
keywords = {Proceedings, Quantum algorithms, Quantum information theory, Simulation of quantum systems},
pubstate = {published},
tppubtype = {Talk}
}
The optimal control problem for open quantum systems can be formulated as a time- dependent Lindbladian that is parameterized by a number of time-dependent control variables. Given an observable and an initial state, the goal is to tune the control variables so that the expected value of some observable with respect to the final state is maximized. In this paper, we present algorithms for solving this optimal control problem efficiently, i.e., having a poly-logarithmic dependency on the system dimension, which is exponentially faster than best-known classical algorithms. Our algorithms are hybrid, consisting of both quantum and classical components. The quantum procedure simulates time-dependent Lindblad evolution that drives the initial state to the final state, and it also provides access to the gradients of the objective function via quantum gradient estimation. The classical procedure uses the gradient information to update the control variables. At the technical level, we provide the first (to the best of our knowledge) simulation al- gorithm for time-dependent Lindbladians with an ℓ1-norm dependence. As an alternative, we also present a simulation algorithm in the interaction picture to improve the algorithm for the cases where the time-independent component of a Lindbladian dominates the time-dependent part. On the classical side, we heavily adapt the state-of-the-art classical optimization analysis to interface with the quantum part of our algorithms. Both the quantum simulation techniques and the classical optimization analyses might be of independent interest
4.
Joseph Cunningham, Jérémie Roland
Eigenpath traversal by Poisson-distributed phase randomisation Talk
2024.
Abstract | Tags: Models of quantum computation, Proceedings, Quantum algorithms
@Talk{T24_194,
title = {Eigenpath traversal by Poisson-distributed phase randomisation},
author = {Joseph Cunningham and Jérémie Roland},
year = {2024},
date = {2024-01-01},
abstract = {We present a framework for quantum computation, similar to Adiabatic Quantum Computation (AQC), that is based on the quantum Zeno effect. By performing randomised dephasing operations at intervals determined by a Poisson process, we are able to track the eigenspace associated to a particular eigenvalue. We derive a simple differential equation for the fidelity leading to general theorems bounding the time complexity of a whole class of algorithms. We also use eigenstate filtering to optimise the scaling of the complexity in the error tolerance ε. In many cases the bounds given by our general theorems are optimal, giving a time complexity of O(1/Δ) with Δ the minimum of the gap. This allows us to prove optimal results using very general features of problems, minimising the amount of problem-specific insight necessary. As two applications of our framework we obtain optimal scaling for the Grover problem (i.e. O(N^1/2) where N is the database size) and the Quantum Linear System Problem (i.e. O(κłog(1/ε)) where κ is the condition number and ε the error tolerance) by direct applications of our theorems.},
keywords = {Models of quantum computation, Proceedings, Quantum algorithms},
pubstate = {published},
tppubtype = {Talk}
}
We present a framework for quantum computation, similar to Adiabatic Quantum Computation (AQC), that is based on the quantum Zeno effect. By performing randomised dephasing operations at intervals determined by a Poisson process, we are able to track the eigenspace associated to a particular eigenvalue. We derive a simple differential equation for the fidelity leading to general theorems bounding the time complexity of a whole class of algorithms. We also use eigenstate filtering to optimise the scaling of the complexity in the error tolerance ε. In many cases the bounds given by our general theorems are optimal, giving a time complexity of O(1/Δ) with Δ the minimum of the gap. This allows us to prove optimal results using very general features of problems, minimising the amount of problem-specific insight necessary. As two applications of our framework we obtain optimal scaling for the Grover problem (i.e. O(N^1/2) where N is the database size) and the Quantum Linear System Problem (i.e. O(κłog(1/ε)) where κ is the condition number and ε the error tolerance) by direct applications of our theorems.
5.
Jordi Weggemans, Marten Folkertsma, Chris Cade
Guidable Local Hamiltonian Problems with Implications to Heuristic Ansatz State Preparation and the Quantum PCP Conjecture Talk
2024.
Abstract | Tags: Proceedings, Quantum complexity theory
@Talk{T24_284,
title = {Guidable Local Hamiltonian Problems with Implications to Heuristic Ansatz State Preparation and the Quantum PCP Conjecture},
author = {Jordi Weggemans and Marten Folkertsma and Chris Cade},
year = {2024},
date = {2024-01-01},
abstract = {We study `Merlinized' versions of the recently defined Guided Local Hamiltonian problem, which we call `Guidable Local Hamiltonian' problems. Unlike their guided counterparts, these problems do not have a guiding state provided as a part of the input, but merely come with the promise that one exists. We consider in particular two classes of guiding states: those that can be prepared efficiently by a quantum circuit; and those belonging to a class of quantum states we call classically evaluatable, for which it is possible to efficiently compute expectation values of local observables classically. We show that guidable local Hamiltonian problems for both classes of guiding states are $QCMA$-complete in the inverse-polynomial precision setting, but lie within $NP$ (or $NqP$) in the constant precision regime when the guiding state is classically evaluatable. Our completeness results show that, from a complexity-theoretic perspective, classical Ansätze selected by classical heuristics are just as powerful as quantum Ansätze prepared by quantum heuristics, as long as one has access to quantum phase estimation. In relation to the quantum PCP conjecture, we (i) define a complexity class capturing quantum-classical probabilistically checkable proof systems and show that it is contained in $BQP^NP[1]$ for constant proof queries; (ii) give a no-go result on `dequantizing' the known quantum reduction which maps a $QPCP$-verification circuit to a local Hamiltonian with constant promise gap; (iii) give several no-go results for the existence of quantum gap amplification procedures that preserve certain ground state properties; and (iv) propose two conjectures that can be viewed as stronger versions of the NLTS theorem. Finally, we show that many of our results can be directly modified to obtain similar results for the class $MA$.},
keywords = {Proceedings, Quantum complexity theory},
pubstate = {published},
tppubtype = {Talk}
}
We study `Merlinized' versions of the recently defined Guided Local Hamiltonian problem, which we call `Guidable Local Hamiltonian' problems. Unlike their guided counterparts, these problems do not have a guiding state provided as a part of the input, but merely come with the promise that one exists. We consider in particular two classes of guiding states: those that can be prepared efficiently by a quantum circuit; and those belonging to a class of quantum states we call classically evaluatable, for which it is possible to efficiently compute expectation values of local observables classically. We show that guidable local Hamiltonian problems for both classes of guiding states are $QCMA$-complete in the inverse-polynomial precision setting, but lie within $NP$ (or $NqP$) in the constant precision regime when the guiding state is classically evaluatable. Our completeness results show that, from a complexity-theoretic perspective, classical Ansätze selected by classical heuristics are just as powerful as quantum Ansätze prepared by quantum heuristics, as long as one has access to quantum phase estimation. In relation to the quantum PCP conjecture, we (i) define a complexity class capturing quantum-classical probabilistically checkable proof systems and show that it is contained in $BQP^NP[1]$ for constant proof queries; (ii) give a no-go result on `dequantizing' the known quantum reduction which maps a $QPCP$-verification circuit to a local Hamiltonian with constant promise gap; (iii) give several no-go results for the existence of quantum gap amplification procedures that preserve certain ground state properties; and (iv) propose two conjectures that can be viewed as stronger versions of the NLTS theorem. Finally, we show that many of our results can be directly modified to obtain similar results for the class $MA$.
6.
Allyson Silva, Xiangyi Zhang, Zachary Webb, Mia Kramer, Chan Woo Yang, Xiao Liu, Jessica Lemieux, Kawai Chen, Artur Scherer, Pooya Ronagh
Multi-qubit Lattice Surgery Scheduling Talk
2024.
Abstract | Tags: Proceedings, Quantum error correction and fault-tolerant quantum computing
@Talk{T24_426,
title = {Multi-qubit Lattice Surgery Scheduling},
author = {Allyson Silva and Xiangyi Zhang and Zachary Webb and Mia Kramer and Chan Woo Yang and Xiao Liu and Jessica Lemieux and Kawai Chen and Artur Scherer and Pooya Ronagh},
year = {2024},
date = {2024-01-01},
abstract = {Fault-tolerant quantum computation using two-dimensional topological quantum error correcting codes can benefit from multi-qubit long-range operations. By using simple commutation rules, a quantum circuit can be transpiled into a sequence of solely non-Clifford multi-qubit gates. Prior work on fault-tolerant compilation avoids optimal scheduling of such gates since they reduce the parallelizability of the circuit. We first show that, using the tableau representation of Clifford gates, this transpilation can be run in linear time with respect to the circuit length, and observe that the reduced parallelization potential is outweighed by the significant reduction in the number of gates. We therefore devise a method for scheduling multi-qubit lattice surgery using an earliest-available-first policy, solving the associated forest packing problem using a representation of the multi-qubit gates as Steiner trees. Our extensive testing on random and real-world circuits demonstrates the method's scalability and performance. We show that the transpilation reduces the circuit length by 82% on average, and that the resulting circuit of multi-qubit gates has an average reduction of 20.5% in the expected circuit execution time compared to serial execution.},
keywords = {Proceedings, Quantum error correction and fault-tolerant quantum computing},
pubstate = {published},
tppubtype = {Talk}
}
Fault-tolerant quantum computation using two-dimensional topological quantum error correcting codes can benefit from multi-qubit long-range operations. By using simple commutation rules, a quantum circuit can be transpiled into a sequence of solely non-Clifford multi-qubit gates. Prior work on fault-tolerant compilation avoids optimal scheduling of such gates since they reduce the parallelizability of the circuit. We first show that, using the tableau representation of Clifford gates, this transpilation can be run in linear time with respect to the circuit length, and observe that the reduced parallelization potential is outweighed by the significant reduction in the number of gates. We therefore devise a method for scheduling multi-qubit lattice surgery using an earliest-available-first policy, solving the associated forest packing problem using a representation of the multi-qubit gates as Steiner trees. Our extensive testing on random and real-world circuits demonstrates the method's scalability and performance. We show that the transpilation reduces the circuit length by 82% on average, and that the resulting circuit of multi-qubit gates has an average reduction of 20.5% in the expected circuit execution time compared to serial execution.
7.
Tomoyuki Morimae, Takashi Yamakawa
One-Wayness in Quantum Cryptography Talk
2024.
Abstract | Tags: Proceedings, Quantum cryptography
@Talk{T24_12,
title = {One-Wayness in Quantum Cryptography},
author = {Tomoyuki Morimae and Takashi Yamakawa},
year = {2024},
date = {2024-01-01},
abstract = {The existence of one-way functions is one of the most fundamental assumptions in classical cryptography. In the quantum world, on the other hand, there are evidences that some cryptographic primitives can exist even if one-way functions do not exist [Kretschmer, TQC 2021; Morimae and Yamakawa, CRYPTO 2022; Ananth, Qian, and Yuen, CRYPTO 2022]. We therefore have the following important open problem in quantum cryptography: What is the most fundamental assumption in quantum cryptography? In this direction, [Brakerski, Canetti, and Qian, ITCS 2023] recently defined a notion called EFI pairs, which are pairs of efficiently generatable states that are statistically distinguishable but computationally indistinguishable, and showed its equivalence with some cryptographic primitives including commitments, oblivious transfer, and general multi-party computations. However, their work focuses on decision-type primitives and does not cover search-type primitives like quantum money and digital signatures. In this paper, we study properties of one-way state generators (OWSGs), which are a quantum analogue of one-way functions proposed by Morimae and Yamakawa. We first revisit the definition of OWSGs and generalize it by allowing mixed output states. Then we show the following results. 1. We define a weaker version of OWSGs, which we call weak OWSGs, and show that they are equivalent to OWSGs. It is a quantum analogue of the amplification theorem for classical weak one-way functions. 2. (Bounded-time-secure) quantum digital signatures with quantum public keys are equivalent to OWSGs. 3. Private-key quantum money schemes (with pure money states) imply OWSGs. 4. Quantum pseudo one-time pad schemes imply both OWSGs and EFI pairs. For EFI pairs, single-copy security suffices. 5. We introduce an incomparable variant of OWSGs, which we call secretly-verifiable and statisticallyinvertible OWSGs, and show that they are equivalent to EFI pairs.},
keywords = {Proceedings, Quantum cryptography},
pubstate = {published},
tppubtype = {Talk}
}
The existence of one-way functions is one of the most fundamental assumptions in classical cryptography. In the quantum world, on the other hand, there are evidences that some cryptographic primitives can exist even if one-way functions do not exist [Kretschmer, TQC 2021; Morimae and Yamakawa, CRYPTO 2022; Ananth, Qian, and Yuen, CRYPTO 2022]. We therefore have the following important open problem in quantum cryptography: What is the most fundamental assumption in quantum cryptography? In this direction, [Brakerski, Canetti, and Qian, ITCS 2023] recently defined a notion called EFI pairs, which are pairs of efficiently generatable states that are statistically distinguishable but computationally indistinguishable, and showed its equivalence with some cryptographic primitives including commitments, oblivious transfer, and general multi-party computations. However, their work focuses on decision-type primitives and does not cover search-type primitives like quantum money and digital signatures. In this paper, we study properties of one-way state generators (OWSGs), which are a quantum analogue of one-way functions proposed by Morimae and Yamakawa. We first revisit the definition of OWSGs and generalize it by allowing mixed output states. Then we show the following results. 1. We define a weaker version of OWSGs, which we call weak OWSGs, and show that they are equivalent to OWSGs. It is a quantum analogue of the amplification theorem for classical weak one-way functions. 2. (Bounded-time-secure) quantum digital signatures with quantum public keys are equivalent to OWSGs. 3. Private-key quantum money schemes (with pure money states) imply OWSGs. 4. Quantum pseudo one-time pad schemes imply both OWSGs and EFI pairs. For EFI pairs, single-copy security suffices. 5. We introduce an incomparable variant of OWSGs, which we call secretly-verifiable and statisticallyinvertible OWSGs, and show that they are equivalent to EFI pairs.
8.
Jiachen Hu, Tongyang Li, Xinzhao Wang, Yecheng Xue, Chenyi Zhang, Han Zhong
Quantum Non-Identical Mean Estimation: Efficient Algorithms and Fundamental Limits Talk
2024.
Abstract | Tags: Proceedings, Quantum algorithms
@Talk{T24_281,
title = {Quantum Non-Identical Mean Estimation: Efficient Algorithms and Fundamental Limits},
author = {Jiachen Hu and Tongyang Li and Xinzhao Wang and Yecheng Xue and Chenyi Zhang and Han Zhong},
year = {2024},
date = {2024-01-01},
abstract = {We systematically investigate quantum algorithms and lower bounds for mean estimation given query access to non-identically distributed samples. On the one hand, we give quantum mean estimators with quadratic quantum speed-up given samples from different bounded or sub-Gaussian random variables. On the other hand, we prove that, in general, it is impossible for any quantum algorithm to achieve quadratic speed-up over the number of classical samples needed to estimate the mean μ, where the samples come from different random variables with mean close to μ. Technically, our quantum algorithms reduce bounded and sub-Gaussian random variables to the Bernoulli case, and use an uncomputation trick to overcome the challenge that direct amplitude estimation does not work with non-identical query access. Our quantum query lower bounds are established by simulating non-identical oracles by parallel oracles, and also by an adversarial method with non-identical oracles. Both results pave the way for proving quantum query lower bounds with non-identical oracles in general, which may be of independent interest.},
keywords = {Proceedings, Quantum algorithms},
pubstate = {published},
tppubtype = {Talk}
}
We systematically investigate quantum algorithms and lower bounds for mean estimation given query access to non-identically distributed samples. On the one hand, we give quantum mean estimators with quadratic quantum speed-up given samples from different bounded or sub-Gaussian random variables. On the other hand, we prove that, in general, it is impossible for any quantum algorithm to achieve quadratic speed-up over the number of classical samples needed to estimate the mean μ, where the samples come from different random variables with mean close to μ. Technically, our quantum algorithms reduce bounded and sub-Gaussian random variables to the Bernoulli case, and use an uncomputation trick to overcome the challenge that direct amplitude estimation does not work with non-identical query access. Our quantum query lower bounds are established by simulating non-identical oracles by parallel oracles, and also by an adversarial method with non-identical oracles. Both results pave the way for proving quantum query lower bounds with non-identical oracles in general, which may be of independent interest.
9.
Tomoyuki Morimae, Alexander Poremba, Takashi Yamakawa
Revocable Quantum Digital Signatures Talk
2024.
Abstract | Tags: Proceedings, Quantum cryptography
@Talk{T24_192,
title = {Revocable Quantum Digital Signatures},
author = {Tomoyuki Morimae and Alexander Poremba and Takashi Yamakawa},
year = {2024},
date = {2024-01-01},
abstract = {We study digital signatures with revocation capabilities and show two results. First, we define and construct digital signatures with revocable signing keys from the LWE assumption. In this primitive, the signing key is a quantum state which enables a user to sign many messages and yet, the quantum key is also revocable, i.e., it can be collapsed into a classical certificate which can later be verified. Once the key is successfully revoked, we require that the initial recipient of the key loses the ability to sign. We construct digital signatures with revocable signing keys from a newly introduced primitive which we call two-tier one-shot signatures, which may be of independent interest. This is a variant of one-shot signatures, where the verification of a signature for the message ``0'' is done publicly, whereas the verification for the message ``1'' is done in private. We give a construction of two-tier one-shot signatures from the LWE assumption. As a complementary result, we also construct digital signatures with quantum revocation from group actions, where the quantum signing key is simply ``returned'' and then verified as part of revocation. Second, we define and construct digital signatures with revocable signatures from OWFs. In this primitive, the signer can produce quantum signatures which can later be revoked. Here, the security property requires that, once revocation is successful, the initial recipient of the signature loses the ability to find accepting inputs to the signature verification algorithm. We construct this primitive using a newly introduced two-tier variant of tokenized signatures. For the construction, we show a new lemma which we call the adaptive hardcore bit property for OWFs, which may enable further applications.},
keywords = {Proceedings, Quantum cryptography},
pubstate = {published},
tppubtype = {Talk}
}
We study digital signatures with revocation capabilities and show two results. First, we define and construct digital signatures with revocable signing keys from the LWE assumption. In this primitive, the signing key is a quantum state which enables a user to sign many messages and yet, the quantum key is also revocable, i.e., it can be collapsed into a classical certificate which can later be verified. Once the key is successfully revoked, we require that the initial recipient of the key loses the ability to sign. We construct digital signatures with revocable signing keys from a newly introduced primitive which we call two-tier one-shot signatures, which may be of independent interest. This is a variant of one-shot signatures, where the verification of a signature for the message ``0'' is done publicly, whereas the verification for the message ``1'' is done in private. We give a construction of two-tier one-shot signatures from the LWE assumption. As a complementary result, we also construct digital signatures with quantum revocation from group actions, where the quantum signing key is simply ``returned'' and then verified as part of revocation. Second, we define and construct digital signatures with revocable signatures from OWFs. In this primitive, the signer can produce quantum signatures which can later be revoked. Here, the security property requires that, once revocation is successful, the initial recipient of the signature loses the ability to find accepting inputs to the signature verification algorithm. We construct this primitive using a newly introduced two-tier variant of tokenized signatures. For the construction, we show a new lemma which we call the adaptive hardcore bit property for OWFs, which may enable further applications.
10.
Yiyi Cai, Yu Tong, John Preskill
Stochastic error cancellation in analog quantum simulation Talk
2024.
Abstract | Tags: Proceedings, Simulation of quantum systems
@Talk{T24_58,
title = {Stochastic error cancellation in analog quantum simulation},
author = {Yiyi Cai and Yu Tong and John Preskill},
year = {2024},
date = {2024-01-01},
abstract = {Analog quantum simulation is a promising path towards solving classically intractable problems in many-body physics on near-term quantum devices. However, the presence of noise limits the size of the system and the length of time that can be simulated. In our work, we consider an error model in which the actual Hamiltonian of the simulator differs from the target Hamiltonian we want to simulate by small local perturbations, which are assumed to be random and unbiased. We analyze the error accumulated in observables in this setting and show that, due to stochastic error cancellation, with high probability the error scales as the square root of the number of qubits instead of linearly. We explore the concentration phenomenon of this error as well as its implications for local observables in the thermodynamic limit. Moreover, we show that stochastic error cancellation also manifests in the fidelity between the target state at the end of time-evolution and the actual state we obtain in the presence of noise. This indicates that, to reach a certain fidelity, more noise can be tolerated than implied by the worst-case bound if the noise comes from many statistically independent sources.},
keywords = {Proceedings, Simulation of quantum systems},
pubstate = {published},
tppubtype = {Talk}
}
Analog quantum simulation is a promising path towards solving classically intractable problems in many-body physics on near-term quantum devices. However, the presence of noise limits the size of the system and the length of time that can be simulated. In our work, we consider an error model in which the actual Hamiltonian of the simulator differs from the target Hamiltonian we want to simulate by small local perturbations, which are assumed to be random and unbiased. We analyze the error accumulated in observables in this setting and show that, due to stochastic error cancellation, with high probability the error scales as the square root of the number of qubits instead of linearly. We explore the concentration phenomenon of this error as well as its implications for local observables in the thermodynamic limit. Moreover, we show that stochastic error cancellation also manifests in the fidelity between the target state at the end of time-evolution and the actual state we obtain in the presence of noise. This indicates that, to reach a certain fidelity, more noise can be tolerated than implied by the worst-case bound if the noise comes from many statistically independent sources.
11.
André Chailloux, Jean-Pierre Tillich
The Quantum Decoding Problem Talk
2024.
Abstract | Tags: Proceedings, Quantum algorithms, Quantum information theory
@Talk{T24_222,
title = {The Quantum Decoding Problem},
author = {André Chailloux and Jean-Pierre Tillich},
year = {2024},
date = {2024-01-01},
abstract = {One of the founding results of lattice based cryptography is a quantum reduction from the Short Integer Solution (SIS) problem to the Learning with Errors (LWE) problem introduced by Regev. It has recently been pointed out by Chen, Liu and Zhandry[CLZ22] that this reduction can be made more powerful by replacing the LWE problem with a quantum equivalent, where the errors are given in quantum superposition. In parallel, Regev's reduction has recently been adapted in the context of code-based cryptography by Debris, Remaud and Tillich[DRT23], who showed a reduction between the Short Codeword Problem and the Decoding Problem (the DRT reduction). This motivates the study of the Quantum Decoding Problem (QDP), which is the Decoding Problem but with errors in quantum superposition and see how it behaves in the DRT reduction. The purpose of this paper is to introduce and to lay a firm foundation for QDP. We first show QD Pis likely to be easier than classical decoding, by proving that it can be solved in quantum polynomial time in a large regime of noise whereas no non-exponential quantum algorithm is known for the classical decoding problem. Then, we show that QDP can even be solved (albeit not necessarily efficiently) beyond the information theoretic Shannon limit for classical decoding. We give precisely the largest noise level where we can solve QDP giving in a sense the information theoretic limit for this new problem. Finally, we study how QDP can be used in the DRT reduction. First, we show that our algorithms can be properly used in the DRT reduction showing that our quantum algorithms for QDP beyond Shannon capacity can be used to find minimal weight codewords in a random code. On the negative side, we show that the DRT reduction cannot be, in all generality, a reduction between finding small codewords and QDP by exhibiting quantum algorithms for QDP where this reduction entirely fails. Our proof techniques include the use of specific quantum measurements, such as q-ary unambiguous state discrimination and pretty good measurements as well as strong concentration bounds on weight distribution of random shifted dual codes, which we relate using quantum Fourier analysis.},
keywords = {Proceedings, Quantum algorithms, Quantum information theory},
pubstate = {published},
tppubtype = {Talk}
}
One of the founding results of lattice based cryptography is a quantum reduction from the Short Integer Solution (SIS) problem to the Learning with Errors (LWE) problem introduced by Regev. It has recently been pointed out by Chen, Liu and Zhandry[CLZ22] that this reduction can be made more powerful by replacing the LWE problem with a quantum equivalent, where the errors are given in quantum superposition. In parallel, Regev's reduction has recently been adapted in the context of code-based cryptography by Debris, Remaud and Tillich[DRT23], who showed a reduction between the Short Codeword Problem and the Decoding Problem (the DRT reduction). This motivates the study of the Quantum Decoding Problem (QDP), which is the Decoding Problem but with errors in quantum superposition and see how it behaves in the DRT reduction. The purpose of this paper is to introduce and to lay a firm foundation for QDP. We first show QD Pis likely to be easier than classical decoding, by proving that it can be solved in quantum polynomial time in a large regime of noise whereas no non-exponential quantum algorithm is known for the classical decoding problem. Then, we show that QDP can even be solved (albeit not necessarily efficiently) beyond the information theoretic Shannon limit for classical decoding. We give precisely the largest noise level where we can solve QDP giving in a sense the information theoretic limit for this new problem. Finally, we study how QDP can be used in the DRT reduction. First, we show that our algorithms can be properly used in the DRT reduction showing that our quantum algorithms for QDP beyond Shannon capacity can be used to find minimal weight codewords in a random code. On the negative side, we show that the DRT reduction cannot be, in all generality, a reduction between finding small codewords and QDP by exhibiting quantum algorithms for QDP where this reduction entirely fails. Our proof techniques include the use of specific quantum measurements, such as q-ary unambiguous state discrimination and pretty good measurements as well as strong concentration bounds on weight distribution of random shifted dual codes, which we relate using quantum Fourier analysis.
