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Single-photon heralded two-qubit unitary gates for pairs of nitrogen-vacancy centers in diamond
摘要： The implementation of a high-fidelity two-qubit quantum logic gate remains an outstanding challenge for isolated solid-state qubits such as nitrogen-vacancy (NV) centers in diamond. In this work, we show that by driving pairs of NV centers to undergo photon scattering processes that flip their qubit states simultaneously, we can achieve a unitary two-qubit gate conditioned upon a single photon-detection event. Further, by exploiting quantum interference between the optical transitions of the NV centers’ electronic states, we realize the existence of two special drive frequencies: a “magic” point where the spin-preserving elastic scattering rates are suppressed and a “balanced” point where the state-flipping scattering rates are equal. We analyzed four different gate operation schemes that utilize these two special drive frequencies, and various combinations of polarizations in the drive and collection paths. Our theoretical and numerical calculations show that the gate fidelity can be as high as 98%. The proposed unitary gate, combined with available single-qubit unitary operations, forms a universal gate set for quantum computing.
关键词： photon scattering,quantum computing,nitrogen-vacancy centers,two-qubit gate,quantum interference
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Bangalore, India (2018.9.19-2018.9.22)] 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Quantum Spider Monkey Optimization (QSMO) Algorithm for Automatic Gray-Scale Image Clustering
摘要： In automatic image clustering, high homogeneity of each cluster is always desired. The increase in number of thresholds in gray scale image segmentation/clustering poses various challenges. Recent times have witnessed the growing popularity of swarm intelligence based algorithms in the field of image segmentation. The Spider Monkey Optimization (SMO) algorithm is a notable example, which is motivated by the intelligent behavior of the spider monkeys. The SMO is broadly categorized as a fission-fusion social structure based intelligent algorithm. The original version of the algorithm as well as its variants have been successfully used in several optimization problems. The current work proposes a quantum version of SMO algorithm which takes recourse to quantum encoding of its population along with quantum variants of the intrinsic operations. The basic concepts and principles of quantum mechanics allows QMSO to explore the power of computing. In QMSO, qubits designated chromosomes operate to drive the solution toward better convergence incorporating rotation gate in Hilbert hyperspace. A fitness function associated with maximum distance between cluster centers have been introduced. An application of the proposed QSMO algorithm is demonstrated on the determination of automatic clusters from real life images. A comparative study with the performance of the classical SMO shows the efficacy of the proposed QSMO algorithm.
关键词： automatic clustering,quantum computing,quantum spider monkey optimization,Clustering,spider monkey optimization
更新于2025-09-09 09:28:46
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Hard limits on the postselectability of optical graph states
摘要： Coherent control of large entangled graph states enables a wide variety of quantum information processing tasks, including error-corrected quantum computation. The linear optical approach offers excellent control and coherence, but today most photon sources and entangling gates—required for the construction of large graph states—are probabilistic and rely on postselection. In this work, we provide proofs and heuristics to aid experimental design using postselection. We introduce a versatile design rule for postselectable experiments: drawn as a graph, with qubit as vertices and gates and photon-pair sources as edges, an experiment may only contain cycles with an odd number of sources. We analyse experiments that use photons from postselected photon-pair sources, and lower bound the number of accessible classes of graph state entanglement in the non-degenerate case—graph state entanglement classes that contain a tree are are always accessible. The proportion of graph states accessible by postselection shrinks rapidly, however. We list accessible classes for various resource states up to 9 qubits. Finally, we apply these methods to near-term multi-photon experiments.
关键词： photon sources,entanglement,graph states,linear optical quantum computing,postselection,numerical methods,photonic experiment design
更新于2025-09-09 09:28:46
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Delivering on a quantum promise
摘要： With the European Commission investing €1bn over 10 years in quantum technologies, Karl Svozil warns against overselling many of the initiative’s longer-term goals. Unlike modern-day politicians, scientists have great authority regarding the pursuit of truth. As a consequence, many members of the public – as well as political bodies and institutions – tend to uncritically take science as a matter of fact. Yet there are some occasions where the benefits and risks of science need to be communicated carefully. A striking example is nuclear energy and the bold claims made by some that nuclear-fission technology is “safe beyond doubt”. One only has to look at the nuclear power plants at Three Mile Island, Chernobyl and Fukushima to know that such claims can prove spurious. In a similar fashion, I believe that the alleged applications of quantum physics are, in some cases, being oversold to the public. The “quantum mechanics is magic” tour – expressed through European physicists’ “quantum manifesto” – has resulted in the European Commission launching a €1bn quantum-technologies flagship initiative in quantum technology. The campaign promises to deliver nothing less than a “second quantum revolution”.
关键词： quantum computing,quantum manifesto,quantum cryptography,quantum technologies,quantum revolution
更新于2025-09-04 15:30:14
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Two-photon self-Kerr nonlinearities for quantum computing and quantum optics
摘要： The self-Kerr interaction is an optical nonlinearity that produces a phase shift proportional to the square of the number of photons in the field. At present, many proposals use nonlinearities to generate photon-photon interactions. For propagating fields these interactions result in undesirable features such as spectral correlation between the photons. Here we engineer a discrete network composed of cross-Kerr interaction regions to simulate a self-Kerr medium. The medium has effective long-range interactions implemented in a physically local way. We compute the one- and two-photon S matrices for fields propagating in this medium. From these scattering matrices we show that our proposal leads to a high-fidelity photon-photon gate. In the limit where the number of nodes in the network tends to infinity, the medium approximates a perfect self-Kerr interaction in the one- and two-photon regime.
关键词： quantum computing,quantum optics,photon-photon gate,cross-Kerr interaction,self-Kerr interaction
更新于2025-09-04 15:30:14
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Computational Speedups Using Small Quantum Devices
摘要： Suppose we have a small quantum computer with only M qubits. Can such a device genuinely speed up certain algorithms, even when the problem size is much larger than M? Here we answer this question to the affirmative. We present a hybrid quantum-classical algorithm to solve 3-satisfiability problems involving n ? M variables that significantly speeds up its fully classical counterpart. This question may be relevant in view of the current quest to build small quantum computers.
关键词： quantum computing,hybrid algorithm,computational speedup,3-satisfiability
更新于2025-09-04 15:30:14
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High-Fidelity Single-Qubit Gates on Neutral Atoms in a Two-Dimensional Magic-Intensity Optical Dipole Trap Array
摘要： As a conventional approach, optical dipole trap (ODT) arrays with linear polarization have been widely used to assemble neutral-atom qubits for building a quantum computer. However, due to the inherent scalar differential light shifts (DLS) of qubit states induced by trapping fields, the microwave-driven gates acting on single qubits suffer from errors on the order of 10?3. Here, we construct a DLS compensated ODT array based upon a recently developed magic-intensity trapping technique. In such a magic-intensity optical dipole trap (MI-ODT) array, the detrimental effects of DLS are efficiently mitigated so that the performance of global microwave-driven Clifford gates is significantly improved. Experimentally, we achieve an average error of e4.7 (cid:2) 1.1T × 10?5 per global gate, which is characterized by randomized benchmarking in a 4 × 4 MI-ODT array. Moreover, we experimentally study the correlation between the coherence time and gate errors in a single MI-ODT with an optimum error per gate of e3.0 (cid:2) 0.7T × 10?5. Our demonstration shows that MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.
关键词： quantum computing,microwave-driven gates,optical dipole trap,magic-intensity trapping,neutral-atom qubits
更新于2025-09-04 15:30:14