QuantumPub Date : 2025-09-24DOI: 10.22331/q-2025-09-24-1862
Francesco Mazzoncini, Balthazar Bauer, Peter Brown, Romain Alléaume
{"title":"Hybrid Quantum Cryptography from Communication Complexity","authors":"Francesco Mazzoncini, Balthazar Bauer, Peter Brown, Romain Alléaume","doi":"10.22331/q-2025-09-24-1862","DOIUrl":"https://doi.org/10.22331/q-2025-09-24-1862","url":null,"abstract":"We introduce an explicit construction for a key distribution protocol in the Quantum Computational Timelock (QCT) security model, where one assumes that computationally secure encryption may only be broken after a time much longer than the coherence time of available quantum memories.<br/> Taking advantage of the QCT assumptions, we build a key distribution protocol called HM-QCT from the Hidden Matching problem for which there exists an exponential gap in one-way communication complexity between classical and quantum strategies.<br/> We establish that the security of HM-QCT against arbitrary i.i.d. attacks can be reduced to the difficulty of solving the underlying Hidden Matching problem with classical information. Legitimate users, on the other hand, can use quantum communication, which gives them the possibility of sending multiple copies of the same quantum state while retaining an information advantage. This leads to an everlasting secure key distribution scheme over $n$ bosonic modes. Such a level of security is unattainable with purely classical techniques. Remarkably, the scheme remains secure with up to $mathcal{O}big( frac{sqrt{n}}{log(n)}big)$ input photons for each channel use, extending the functionalities and potentially outperforming QKD rates by several orders of magnitudes.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"10 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-24DOI: 10.22331/q-2025-09-24-1863
A. Keefe, N. Agarwal, A. Kamal
{"title":"Quantifying spectral signatures of non-Markovianity beyond the Born-Redfield master equation","authors":"A. Keefe, N. Agarwal, A. Kamal","doi":"10.22331/q-2025-09-24-1863","DOIUrl":"https://doi.org/10.22331/q-2025-09-24-1863","url":null,"abstract":"Memory or time-non-local effects in open quantum dynamics pose theoretical as well as practical challenges in the understanding and control of noisy quantum systems. While there has been a comprehensive and concerted effort towards developing diagnostics for non-Markovian dynamics, all existing measures rely on time-domain measurements which are typically slow and expensive as they require averaging several runs to resolve small transient features on a broad background, and scale unfavorably with system size and complexity. In this work, we propose a spectroscopic measure of non-Markovianity which can detect persistent non-Markovianity in the system steady state. In addition to being experimentally viable, the proposed measure has a direct information theoretic interpretation: a large value indicates the information loss per unit bandwidth of making the Markov approximation. In the same vein, we derive a frequency-domain quantum master equation (FD-QME) that goes beyond the standard Born-Redfield description and retains the full memory of the state of the reduced system. Using the FD-QME and the proposed measure, we are able to reliably diagnose and quantify non-Markovianity in several system-environment settings including those with environmental correlations and retardation effects.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-24DOI: 10.22331/q-2025-09-24-1864
Xuan Du Trinh, Nengkun Yu
{"title":"Adaptivity is not helpful for Pauli channel learning","authors":"Xuan Du Trinh, Nengkun Yu","doi":"10.22331/q-2025-09-24-1864","DOIUrl":"https://doi.org/10.22331/q-2025-09-24-1864","url":null,"abstract":"We prove that adaptive strategies offer no advantage over non-adaptive ones for learning and testing Pauli channels using entangled inputs. This key observation allows us to characterize the query complexity for several fundamental tasks by translating optimal classical estimation algorithms into the quantum setting. First, we determine the tight query complexity for learning a Pauli channel under the general $ell_p$ norm, providing results that improve upon or match the best-known bounds for the $ell_1, ell_2,$ and $ell_infty$ distances. Second, we resolve the complexity of testing whether a Pauli channel is a white noise source. Finally, we show that the optimal query complexities for estimating the Shannon entropy and support size of the channel's error distribution, and for estimating the diamond distance between two Pauli channels, are all $Thetaleft(tfrac{4^n}{nepsilon^2}right)$.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"13 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-18DOI: 10.22331/q-2025-09-18-1861
Carlos Vega, Alberto Muñoz de las Heras, Diego Porras, Alejandro González-Tudela
{"title":"Topological, multi-mode amplification induced by non-reciprocal, long-range dissipative couplings","authors":"Carlos Vega, Alberto Muñoz de las Heras, Diego Porras, Alejandro González-Tudela","doi":"10.22331/q-2025-09-18-1861","DOIUrl":"https://doi.org/10.22331/q-2025-09-18-1861","url":null,"abstract":"Non-reciprocal couplings or drivings are known to induce steady-state, directional, amplification in driven-dissipative bosonic lattices. This amplification phenomenon has been recently linked to the existence of a non-zero topological invariant defined with the system's dynamical matrix, and thus, it depends critically on the couplings' structure. In this work, we demonstrate the emergence of unconventional, non-reciprocal, long-range dissipative couplings induced by the interaction of the bosonic chain with a chiral, multi-mode channel, and then study their impact on topological amplification phenomena. We show that these couplings can lead to topological invariant values greater than one which induce topological, multi-mode amplification and metastability behaviour. Besides, we also show how these couplings can also display topological amplifying phases that are dynamically stable in the presence of local parametric drivings. Finally, we conclude by showing how such phenomena can be naturally obtained in two-dimensional topological insulators hosting multiple edge modes.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"77 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145077225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-16DOI: 10.22331/q-2025-09-16-1860
Vivien Vandaele
{"title":"Lower T-count with faster algorithms","authors":"Vivien Vandaele","doi":"10.22331/q-2025-09-16-1860","DOIUrl":"https://doi.org/10.22331/q-2025-09-16-1860","url":null,"abstract":"Among the cost metrics characterizing a quantum circuit, the $T$-count stands out as one of the most crucial as its minimization is particularly important in various areas of quantum computation such as fault-tolerant quantum computing and quantum circuit simulation. In this work, we contribute to the $T$-count reduction problem by proposing efficient $T$-count optimizers with low execution times. In particular, we greatly improve the complexity of TODD, an algorithm currently providing the best $T$-count reduction on various quantum circuits. We also propose some modifications to the algorithm which are leading to a significantly lower number of $T$ gates. In addition, we propose another algorithm which has an even lower complexity and that achieves a better or equal $T$-count than the state of the art on most quantum circuits evaluated. We also prove that the number of $T$ gates in the circuit obtained after executing our algorithms on a Hadamard-free circuit composed of $n$ qubits is upper bounded by $n(n + 1)/2 + 1$, which improves on the worst-case $T$-count of existing optimization algorithms. From this we derive an upper bound of $(n + 1)(n + 2h)/2 + 1$ for the number of $T$ gates in a Clifford$+T$ circuit where $h$ is the number of internal Hadamard gates in the circuit, i.e. the number of Hadamard gates lying between the first and the last $T$ gate of the circuit.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"15 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145068057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-16DOI: 10.22331/q-2025-09-16-1859
Stefano Carignano, Luca Tagliacozzo
{"title":"Loschmidt echo, emerging dual unitarity and scaling of generalized temporal entropies after quenches to the critical point","authors":"Stefano Carignano, Luca Tagliacozzo","doi":"10.22331/q-2025-09-16-1859","DOIUrl":"https://doi.org/10.22331/q-2025-09-16-1859","url":null,"abstract":"We show how the Loschmidt echo of a product state after a quench to a conformal invariant critical point and its leading finite time corrections can be predicted by using conformal field theories (CFT). We check such predictions with tensor networks, finding excellent agreement. As a result, we can use the Loschmidt echo to extract the universal information of the underlying CFT including the central charge, the operator content, and its generalized temporal entropies. We are also able to predict and confirm an emerging dual-unitarity of the evolution at late times, since the spatial transfer matrix operator that evolves the system in space becomes unitary in such limit. Our results on the growth of temporal entropies also imply that, using state-of-the art tensor networks algorithms, such calculations only require resources that increase polynomially with the duration of the quench, thus providing an example of numerically efficiently solvable out-of-equilibrium scenario.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"24 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145067921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-15DOI: 10.22331/q-2025-09-15-1858
Yunzhe Zheng, Dong E. Liu
{"title":"From Magic State Distillation to Dynamical Systems","authors":"Yunzhe Zheng, Dong E. Liu","doi":"10.22331/q-2025-09-15-1858","DOIUrl":"https://doi.org/10.22331/q-2025-09-15-1858","url":null,"abstract":"Magic State Distillation (MSD) has been a research focus for fault-tolerant quantum computing due to the need for non-Clifford resource in gaining quantum advantage. Although many of the MSD protocols so far are based on stabilizer codes with transversal $T$ gates, there exists quite several protocols that don't fall into this class. Here we propose a method to map MSD protocols to iterative dynamical systems under the framework of stabilizer reduction. With the proposed mapping, we are able to analyze the performance of MSD protocols using techniques from dynamical systems theory, easily simulate the distillation process of input states under arbitrary noise and visualize it using flow diagram. We apply our mapping to common MSD protocols for $|Trangle$ state and find some interesting properties: The $[[15, 1, 3]]$ code may distill states corresponding to $sqrt{T}$ gate and the $[[5, 1, 3]]$ code can distill the magic state corresponding to the $T$ gate. Besides, we examine the exotic MSD protocols that may distill into other magic states proposed in [Eur. Phys. J. D 70, 55 (2016)] and identify the condition for distillable magic states. We also study new MSD protocols generated by concatenating different codes and numerically demonstrate that concatenation can generate MSD protocols with various magic states. By concatenating efficient codes with exotic codes, we can reduce the overhead of the exotic MSD protocols. We believe our proposed method will be a useful tool for simulating and visualization MSD protocols for canonical MSD protocols on $|Trangle$ as well as other unexplored MSD protocols for other states.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"1 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145059424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-11DOI: 10.22331/q-2025-09-11-1855
Dilip Paneru, Francesco Di Colandrea, Alessio D'Errico, Ebrahim Karimi
{"title":"Nonlocal transfer of high-dimensional unitary operations","authors":"Dilip Paneru, Francesco Di Colandrea, Alessio D'Errico, Ebrahim Karimi","doi":"10.22331/q-2025-09-11-1855","DOIUrl":"https://doi.org/10.22331/q-2025-09-11-1855","url":null,"abstract":"Highly correlated biphoton states are powerful resources in quantum optics, both for fundamental tests of the theory and practical applications. In particular, high-dimensional spatial correlation has been used in several quantum information processing and sensing tasks, for instance, in ghost imaging experiments along with several quantum key distribution protocols. Here, we introduce a technique that exploits spatial correlations, whereby one can nonlocally access the result of an arbitrary unitary operator on an arbitrary input state without the need to perform any operation themselves. The method is experimentally validated on a set of spatially periodic unitary operations in one-dimensional and two-dimensional spaces. Our findings pave the way for efficiently distributing quantum simulations and computations in future instances of quantum networks where users with limited resources can nonlocally access the results of complex unitary transformations via a centrally located quantum processor.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"14 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145031855","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-11DOI: 10.22331/q-2025-09-11-1854
Keith R. Fratus, Kirsten Bark, Nicolas Vogt, Juha Leppäkangas, Sebastian Zanker, Michael Marthaler, Jan-Michael Reiner
{"title":"Describing Trotterized Time Evolutions on Noisy Quantum Computers via Static Effective Lindbladians","authors":"Keith R. Fratus, Kirsten Bark, Nicolas Vogt, Juha Leppäkangas, Sebastian Zanker, Michael Marthaler, Jan-Michael Reiner","doi":"10.22331/q-2025-09-11-1854","DOIUrl":"https://doi.org/10.22331/q-2025-09-11-1854","url":null,"abstract":"We consider the extent to which a Trotterized time evolution implemented on a quantum computer is altered by the presence of decoherence. Given a specific set of assumptions regarding the manner in which noise processes acting on such a device can be modeled at the circuit level, we show how the effects of noise can be reinterpreted as a shift to the dynamics of the original system being simulated. In particular, we find that this shift can be described through the use of static Lindblad noise terms, which act in addition to the original unitary dynamics. The form of these noise terms depends not only on the underlying noise processes occurring on the device, but also on the original unitary dynamics, as well as the manner in which these dynamics are simulated on the device, i.e., the choice of quantum algorithm. We call this effectively simulated open quantum system the noisy algorithm model. Our results are confirmed through numerical analysis.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"37 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145031854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
QuantumPub Date : 2025-09-11DOI: 10.22331/q-2025-09-11-1853
Dorit Aharonov, Alex B. Grilo, Yupan Liu
{"title":"StoqMA vs. MA: the power of error reduction","authors":"Dorit Aharonov, Alex B. Grilo, Yupan Liu","doi":"10.22331/q-2025-09-11-1853","DOIUrl":"https://doi.org/10.22331/q-2025-09-11-1853","url":null,"abstract":"$sf{StoqMA}$ characterizes the computational hardness of stoquastic local Hamiltonians, which is a family of Hamiltonians that does not suffer from the sign problem. Although error reduction is commonplace for many complexity classes, such as $sf{BPP, BQP, MA, QMA}$, etc.,this property remains open for $sf{StoqMA}$ since Bravyi, Bessen and Terhal defined this class in 2006. In this note, we show that error reduction for $sf{StoqMA}$ will imply that $sf{StoqMA = MA}$.","PeriodicalId":20807,"journal":{"name":"Quantum","volume":"42 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145031853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}