Haruki Kiyama, Danny van Hien, Arne Ludwig, Andreas D. Wieck, Akira Oiwa
{"title":"High-fidelity spin readout via the double latching mechanism","authors":"Haruki Kiyama, Danny van Hien, Arne Ludwig, Andreas D. Wieck, Akira Oiwa","doi":"10.1038/s41534-024-00882-1","DOIUrl":"https://doi.org/10.1038/s41534-024-00882-1","url":null,"abstract":"<p>Projective measurement of single-electron spins, or spin readout, is among the most fundamental technologies for spin-based quantum information processing. Implementing spin readout with both high-fidelity and scalability is indispensable for developing fault-tolerant quantum computers in large-scale spin-qubit arrays. To achieve high fidelity, a latching mechanism is useful. However, the fidelity can be decreased by spin relaxation and charge state leakage, and the scalability is currently challenging. Here, we propose and demonstrate a double-latching high-fidelity spin readout scheme, which suppresses errors via an additional latching process. We experimentally show that the double-latching mechanism provides significantly higher fidelity than the conventional latching mechanism and estimate a potential spin readout fidelity of 99.94% using highly spin-dependent tunnel rates. Due to isolation from error-inducing processes, the double-latching mechanism combined with scalable charge readout is expected to be useful for large-scale spin-qubit arrays while maintaining high fidelity.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"1 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142368815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Philipp J. Vetter, Thomas Reisser, Maximilian G. Hirsch, Tommaso Calarco, Felix Motzoi, Fedor Jelezko, Matthias M. Müller
{"title":"Gate-set evaluation metrics for closed-loop optimal control on nitrogen-vacancy center ensembles in diamond","authors":"Philipp J. Vetter, Thomas Reisser, Maximilian G. Hirsch, Tommaso Calarco, Felix Motzoi, Fedor Jelezko, Matthias M. Müller","doi":"10.1038/s41534-024-00893-y","DOIUrl":"https://doi.org/10.1038/s41534-024-00893-y","url":null,"abstract":"<p>A recurring challenge in quantum science and technology is the precise control of their underlying dynamics that lead to the desired quantum operations, often described by a set of quantum gates. These gates can be subject to application-specific errors, leading to a dependence of their controls on the chosen circuit, the quality measure and the gate-set itself. A natural solution would be to apply quantum optimal control in an application-oriented fashion. In turn, this requires the definition of a meaningful measure of the contextual gate-set performance. Therefore, we explore and compare the applicability of quantum process tomography, linear inversion gate-set tomography, randomized linear gate-set tomography, and randomized benchmarking as measures for closed-loop quantum optimal control experiments, using a macroscopic ensemble of nitrogen-vacancy centers in diamond as a test-bed. Our work demonstrates the relative trade-offs between those measures and how to significantly enhance the gate-set performance, leading to an improvement across all investigated methods.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"25 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142363012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Matteo Padovan, Giulio Foletto, Lorenzo Coccia, Marco Avesani, Paolo Villoresi, Giuseppe Vallone
{"title":"Secure and robust randomness with sequential quantum measurements","authors":"Matteo Padovan, Giulio Foletto, Lorenzo Coccia, Marco Avesani, Paolo Villoresi, Giuseppe Vallone","doi":"10.1038/s41534-024-00879-w","DOIUrl":"https://doi.org/10.1038/s41534-024-00879-w","url":null,"abstract":"<p>Quantum correlations between measurements of separated observers are crucial for applications like randomness generation and key distribution. Although device-independent security can be certified with minimal assumptions, current protocols have limited performance. Here, we exploit sequential measurements, defined with a precise temporal order, to enhance performance by reusing quantum states. We provide a geometric perspective and a general mathematical framework, analytically proving a Tsirelson-like boundary for sequential quantum correlations, which represents a trade-off in nonlocality shared by sequential users. This boundary is advantageous for secure quantum randomness generation, certifying maximum bits per state with one remote and two sequential parties, even if one sequential user shares no nonlocality. Our simple qubit protocol reaches this boundary, and numerical analysis shows improved robustness under realistic noise. A photonic implementation confirms feasibility and robustness. This study advances the understanding of sequential quantum correlations and offers insights for efficient device-independent protocols.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"23 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142330333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Allan Tosta, Thais de Lima Silva, Giancarlo Camilo, Leandro Aolita
{"title":"Randomized semi-quantum matrix processing","authors":"Allan Tosta, Thais de Lima Silva, Giancarlo Camilo, Leandro Aolita","doi":"10.1038/s41534-024-00883-0","DOIUrl":"https://doi.org/10.1038/s41534-024-00883-0","url":null,"abstract":"<p>We present a hybrid quantum-classical framework for simulating generic matrix functions more amenable to early fault-tolerant quantum hardware than standard quantum singular-value transformations. The method is based on randomization over the Chebyshev approximation of the target function while keeping the matrix oracle quantum, and is assisted by a variant of the Hadamard test that removes the need for post-selection. The resulting statistical overhead is similar to the fully quantum case and does not incur any circuit depth degradation. On the contrary, the average circuit depth is shown to get smaller, yielding equivalent reductions in noise sensitivity, as explicitly shown for depolarizing noise and coherent errors. We apply our technique to partition-function estimation, linear system solvers, and ground-state energy estimation. For these cases, we prove advantages on average depths, including quadratic speed-ups on costly parameters and even the removal of the approximation-error dependence.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"115 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142330330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Rik Broekhoven, Curie Lee, Soo-hyon Phark, Sander Otte, Christoph Wolf
{"title":"Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope","authors":"Rik Broekhoven, Curie Lee, Soo-hyon Phark, Sander Otte, Christoph Wolf","doi":"10.1038/s41534-024-00888-9","DOIUrl":"https://doi.org/10.1038/s41534-024-00888-9","url":null,"abstract":"<p>Certifying quantum entanglement is a critical step toward realizing quantum-coherent applications. In this work, we show that entanglement of spins can be unambiguously evidenced in a scanning tunneling microscope with electron spin resonance by exploiting the fact that entangled states undergo a free time evolution with a distinct characteristic time constant that clearly distinguishes it from the time evolution of non-entangled states. By implementing a phase control scheme, the phase of this time evolution can be mapped back onto the population of one entangled spin, which can then be read out reliably using a weakly coupled sensor spin in the junction of the scanning tunneling microscope. We demonstrate through open quantum system simulations with currently available spin coherence times of <i>T</i><sub>2</sub> ≈ 300 ns, that a signal directly correlated with the degree of entanglement can be measured at temperatures of 100–400 mK accessible in sub-Kelvin scanning tunneling microscopes.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"25 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142329209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
{"title":"Superdiffusive to ballistic transport in nonintegrable Rydberg simulator","authors":"Chun Chen, Yan Chen, Xiaoqun Wang","doi":"10.1038/s41534-024-00884-z","DOIUrl":"https://doi.org/10.1038/s41534-024-00884-z","url":null,"abstract":"<p>A common wisdom posits that transport of conserved quantities across clean nonintegrable quantum systems at high temperatures is diffusive when probed from the emergent hydrodynamic regime. We show that this empirical paradigm may alter if the strong interaction limit is taken. Using Krylov-typicality and purification matrix-product-state methods, we establish in short-to-intermediate time scales the following observations for the nonintegrable lattice model imitating the experimental Rydberg blockade simulator. Given the strict projection owing to the infinite density-density repulsion <i>V</i>, the Rydberg chain’s energy transport in the presence of a transverse field <i>g</i> is tentatively superdiffusive at infinite temperature featured by an anomalous scaling exponent <span>(frac{3}{4})</span>, indicating the potential existence of a novel dynamical universality class. Imposing, in addition, a growing longitudinal field <i>h</i> causes a putative superdiffusion-to-ballistic transport transition at <i>h</i> ≈ <i>g</i>. Interestingly, all the above results persist for large but finite interactions and temperatures, provided that the strongly interacting condition <i>g</i>, <i>h</i> <span>≪</span> <i>k</i><sub>B</sub><i>T</i> <span>≪</span> <i>V</i> is fulfilled. Our predictions are testable by current Rydberg quantum simulation facilities.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"14 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Stephan Kucera, Christian Haen, Elena Arenskötter, Tobias Bauer, Jonas Meiers, Marlon Schäfer, Ross Boland, Milad Yahyapour, Maurice Lessing, Ronald Holzwarth, Christoph Becher, Jürgen Eschner
{"title":"Demonstration of quantum network protocols over a 14-km urban fiber link","authors":"Stephan Kucera, Christian Haen, Elena Arenskötter, Tobias Bauer, Jonas Meiers, Marlon Schäfer, Ross Boland, Milad Yahyapour, Maurice Lessing, Ronald Holzwarth, Christoph Becher, Jürgen Eschner","doi":"10.1038/s41534-024-00886-x","DOIUrl":"https://doi.org/10.1038/s41534-024-00886-x","url":null,"abstract":"<p>We report on the implementation of quantum entanglement distribution and quantum state teleportation over a 14.4 km urban dark-fiber link, which is partially underground, partially overhead, and patched in several stations. We characterize the link for its use as a quantum channel and realize its active polarization stabilization. Using a type-II cavity-enhanced SPDC photon pair source, a <sup>40</sup>Ca<sup>+</sup> single-ion quantum memory, and quantum frequency conversion to the telecom C-band, we demonstrate photon-photon entanglement, ion-photon entanglement, and teleportation of a qubit state from the ion onto a remote telecom photon, all realized over the urban fiber link.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"44 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142231455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Jiří Fadrný, Michal Neset, Martin Bielak, Miroslav Ježek, Jan Bílek, Jaromír Fiurášek
{"title":"Experimental preparation of multiphoton-added coherent states of light","authors":"Jiří Fadrný, Michal Neset, Martin Bielak, Miroslav Ježek, Jan Bílek, Jaromír Fiurášek","doi":"10.1038/s41534-024-00885-y","DOIUrl":"https://doi.org/10.1038/s41534-024-00885-y","url":null,"abstract":"<p>Conditional addition of photons represents a crucial tool for optical quantum state engineering and it forms a fundamental building block of advanced quantum photonic devices. Here we report on experimental implementation of the conditional addition of several photons. We demonstrate the addition of one, two, and three photons to input coherent states with various amplitudes. The resulting highly nonclassical photon-added states are completely characterized with time-domain homodyne tomography, and the nonclassicality of the prepared states is witnessed by the negativity of their Wigner functions. We experimentally demonstrate that the conditional addition of photons realizes approximate noiseless quantum amplification of coherent states with sufficiently large amplitude. We also investigate certification of the stellar rank of the generated multiphoton-added coherent states, which quantifies the non-Gaussian resources required for their preparation. Our results pave the way towards the experimental realization of complex optical quantum operations based on combination of multiple photon additions and subtractions.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"4 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142231454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
{"title":"An extremely bad-cavity laser","authors":"Jia Zhang, Tiantian Shi, Jianxiang Miao, Deshui Yu, Jingbiao Chen","doi":"10.1038/s41534-024-00880-3","DOIUrl":"https://doi.org/10.1038/s41534-024-00880-3","url":null,"abstract":"<p>Lasing in the bad-cavity regime has promising applications in quantum precision measurement and frequency metrology due to the reduced sensitivity of the laser frequency to cavity-length fluctuations. Thus far, relevant studies have been mainly focused on conventional cavities whose finesse is high enough that the resonance linewidth is sufficiently narrow compared to the cavity’s free spectral range, though still in the bad-cavity regime. However, lasing output from the cavity whose finesse is close to the limit of 2 has never been experimentally accessed. Here, we demonstrate an extremely bad-cavity laser, analyze the physical mechanisms limiting cavity finesse, and report on the worst-ever laser cavity with finesse reaching 2.01. The optical cavity has a reflectance close to zero and only provides weak optical feedback. The laser power can be as high as tens of <i>μ</i>W and the spectral linewidth reaches a few kHz, over one thousand times narrower than the gain bandwidth. In addition, the measurement of cavity pulling reveals a pulling coefficient of 0.0148, the lowest value ever achieved for a continuous-wave laser. Our findings open up an unprecedentedly innovative perspective for future new ultra-stable lasers, which could possibly trigger future discoveries in optical clocks, cavity QED, continuous-wave superradiant laser, and explorations of quantum many-body physics.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"4 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142231456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
Hailan Ma, Gary J. Mooney, Ian R. Petersen, Lloyd C. L. Hollenberg, Daoyi Dong
{"title":"Quantum autoencoders using mixed reference states","authors":"Hailan Ma, Gary J. Mooney, Ian R. Petersen, Lloyd C. L. Hollenberg, Daoyi Dong","doi":"10.1038/s41534-024-00872-3","DOIUrl":"https://doi.org/10.1038/s41534-024-00872-3","url":null,"abstract":"<p>One of the fundamental tasks in quantum information theory is quantum data compression, which can be realized via quantum autoencoders that first compress quantum states to low-dimensional ones and then recover to the original ones with a reference state. When taking a pure reference state, there exists an upper bound for the encoding fidelity, which limits the compression of states with high entropy. To overcome the entropy inconsistency, we allow the reference state to be a mixed state and propose a cost function that combines the encoding fidelity and the quantum mutual information. We consider the reference states to be a mixture of maximally mixed states and pure states and propose three strategies for setting the ratio of mixedness. Numerical simulations of different states and experimental implementations on IBM quantum computers illustrate the effectiveness of our approach.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"61 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142174993","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}