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Journal articles on the topic 'Qubit'

Author: Grafiati

Published: 4 June 2021

Last updated: 25 July 2025

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1

Moussa, Jonathan Edward. "Quantum circuits for qubit fusion." Quantum Information and Computation 16, no. 13&14 (2016): 1113–24. http://dx.doi.org/10.26421/qic16.13-14-3.

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We consider four-dimensional qudits as qubit pairs and their qudit Pauli operators as qubit Clifford operators. This introduces a nesting, C^2_1 belong to C^4_2 belong to C^2_3 , where Cmn is the nth level of the m-dimensional qudit Clifford hierarchy. If we can convert between logical qubits and qudits, then qudit Clifford operators are qubit non-Clifford operators. Conversion is achieved by qubit fusion and qudit fission using stabilizer circuits that consume a resource state. This resource is a fused qubit stabilizer state with a faulttolerant state preparation using stabilizer circuits.

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2

Drozhzhin, Denis A., Anastasiia S. Nikolaeva, Evgeniy O. Kiktenko, and Aleksey K. Fedorov. "Transpiling Quantum Assembly Language Circuits to a Qudit Form." Entropy 26, no. 12 (2024): 1129. https://doi.org/10.3390/e26121129.

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In this paper, we introduce the workflow for converting qubit circuits represented by Open Quantum Assembly format (OpenQASM, also known as QASM) into the qudit form for execution on qudit hardware and provide a method for translating qudit experiment results back into qubit results. We present the comparison of several qudit transpilation regimes, which differ in decomposition of multicontrolled gates: qubit as ordinary qubit transpilation and execution, qutrit with d=3 levels and single qubit in qudit, and ququart with d=4 levels and 2 qubits per ququart. We provide several examples of trans

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3

Nikolaeva, Anstasiia S., Evgeniy O. Kiktenko, and Aleksey K. Fedorov. "Generalized Toffoli Gate Decomposition Using Ququints: Towards Realizing Grover’s Algorithm with Qudits." Entropy 25, no. 2 (2023): 387. http://dx.doi.org/10.3390/e25020387.

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Qubits, which are the quantum counterparts of classical bits, are used as basic information units for quantum information processing, whereas underlying physical information carriers, e.g., (artificial) atoms or ions, admit encoding of more complex multilevel states—qudits. Recently, significant attention has been paid to the idea of using qudit encoding as a way for further scaling quantum processors. In this work, we present an efficient decomposition of the generalized Toffoli gate on five-level quantum systems—so-called ququints—that use ququints’ space as the space of two qubits with a jo

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4

LIU, YANG, GUI LU LONG, and YANG SUN. "ANALYTIC ONE-BIT AND CNOT GATE CONSTRUCTIONS OF GENERAL n-QUBIT CONTROLLED GATES." International Journal of Quantum Information 06, no. 03 (2008): 447–62. http://dx.doi.org/10.1142/s0219749908003621.

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General n-qubit controlled unitary gates are frequently used in quantum information processing tasks. Barenco, Bennett, Cleve, Di Vincenzo, Margolus and Shor [Phys. Rev. A52 (1995) 3457] have given the general construction methods, and explicit results for up-to-four-qubits controlled unitary gates. We extended their calculation and gave two analytic expressions for the construction of general n-qubit controlled unitary gates in terms of one-qubit and two-qubit CNOT gates. There are two expressions – one is exponential in the qubit number which is efficient for up to ten qubits, and the other

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5

DOLL, ROLAND, MARTIJN WUBS, SIGMUND KOHLER, and PETER HÄNGGI. "FIDELITY AND ENTANGLEMENT OF A SPATIALLY EXTENDED LINEAR THREE-QUBIT REGISTER." International Journal of Quantum Information 06, supp01 (2008): 681–87. http://dx.doi.org/10.1142/s0219749908003955.

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We study decoherence of a three-qubit array coupled to substrate phonons. Assuming an initial three-qubit entangled state that would be decoherence-free for identical qubit positions, allows us to focus on non-Markovian effects of the inevitable spatial qubit separation. It turns out that the coherence is most affected when the qubits are regularly spaced. Moreover, we find that up to a constant scaling factor, two-qubit entanglement is not influenced by the presence of the third qubit, even though all qubits interact via the phonon field.

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6

Espinel-López, Cristian, Alvaro Martínez-Gómez, Marisol Aguilar-Echeverría, and Hipatia Mañay-Mañay. "Evolución de componentes de computación cuántica y mediciones cuánticas no destructivas en la informática moderna. //Evolution of quantum computing components and non-destructive quantum measurements in modern computing." CIENCIA UNEMI 11, no. 28 (2018): 57–69. http://dx.doi.org/10.29076/issn.2528-7737vol11iss28.2018pp57-69p.

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El presente trabajo, realiza una breve introducción a las medidas QND (Quantum nondemolition measurement) y sus características. Además, se describe teóricamente un qubit acoplado a un oscilador armónico cuántico forzado como ejemplo de una medición QND en un qubit. El formalismo desarrollado para este tipo de sistemas cuánticos acoplados se desenvuelve dentro de la teoría cuántica de la computación. Como parte del estudio de las mediciones QND, se introducen los qubits de flujo que hacen uso de los interferómetros superconductores cuánticos (SQUIDs). El análisis de este esquema informático in

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7

Schönenberger, Christian. "Andreev‐Qubit‐Qubit‐Kopplung auf Distanz." Physik in unserer Zeit 56, no. 2 (2025): 60–61. https://doi.org/10.1002/piuz.202570205.

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Mikroskopische Andreev‐Qubits lassen sich nun kohärent über makroskopische Distanzen koppeln, was die Erzeugung von verschränkten Zuständen und allgemeinen Zwei‐Qubit‐Operationen ermöglicht. Dies konnte kürzlich sowohl für Andreev‐Paar‐Qubits als auch für Andreev‐Spin‐Qubits demonstriert werden.

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8

Fischer, Laurin E., Alessandro Chiesa, Francesco Tacchino, Daniel J. Egger, Stefano Carretta, and Ivano Tavernelli. "Universal Qudit Gate Synthesis for Transmons." PRX Quantum 4 (August 28, 2023): 030327. https://doi.org/10.1103/PRXQuantum.4.030327.

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Gate-based quantum computers typically encode and process information in two-dimensional units called qubits. Using d-dimensional qudits instead may offer intrinsic advantages, including more efficient circuit synthesis, problem-tailored encodings and embedded error correction. In this work, we design a superconducting qudit-based quantum processor wherein the logical space of transmon qubits is extended to higher-excited levels. We propose a universal gate set featuring a two-qudit cross-resonance entangling gate, for which we predict fidelities beyond 99% in the d =

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9

Childs, Andrew M., Debbie Leung, Laura Mancinska, and Maris Ozols. "Characterization of universal two-qubit Hamiltonians." Quantum Information and Computation 11, no. 1&2 (2011): 19–39. http://dx.doi.org/10.26421/qic11.1-2-3.

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Suppose we can apply a given 2-qubit Hamiltonian H to any (ordered) pair of qubits. We say H is n-universal if it can be used to approximate any unitary operation on n qubits. While it is well known that almost any 2-qubit Hamiltonian is 2-universal, an explicit characterization of the set of non-universal 2-qubit Hamiltonians has been elusive. Our main result is a complete characterization of 2-non-universal 2-qubit Hamiltonians. In particular, there are three ways that a 2-qubit Hamiltonian $H$ can fail to be universal: (1) H shares an eigenvector with the gate that swaps two qubits, (2) H a

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10

Sharma, Ritvik, and Sara Achour. "Optimizing Ancilla-Based Quantum Circuits with SPARE." Proceedings of the ACM on Programming Languages 9, PLDI (2025): 176–200. https://doi.org/10.1145/3729253.

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Many quantum algorithms instantiate and use ancillas, spare qubits that serve as temporary storage in a quantum circuit. In particular, many recently developed high-level and modular quantum programming languages (QPLs) use ancilla qubits to implement various programming constructs. These are lowered to circuits with nested/cascading compute-uncompute gate sequences that use ancilla qubits to track internal state. We present SPARE, a rewrite-based quantum circuit optimizer that restructures these compute-uncompute gate sequences, leveraging the ancilla qubit state information to optimize the c

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11

Assouline, A., L. Pugliese, H. Chakraborti, et al. "Emission and coherent control of Levitons in graphene." Science 382, no. 6676 (2023): 1260–64. http://dx.doi.org/10.1126/science.adf9887.

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Flying qubits encode quantum information in propagating modes instead of stationary discrete states. Although photonic flying qubits are available, the weak interaction between photons limits the efficiency of conditional quantum gates. Conversely, electronic flying qubits can use Coulomb interactions, but the weaker quantum coherence in conventional semiconductors has hindered their realization. In this work, we engineered on-demand injection of a single electronic flying qubit state and its manipulation over the Bloch sphere. The flying qubit is a Leviton propagating in quantum Hall edge cha

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12

Gidney, Craig, Michael Newman, and Matt McEwen. "Benchmarking the Planar Honeycomb Code." Quantum 6 (September 21, 2022): 813. http://dx.doi.org/10.22331/q-2022-09-21-813.

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We improve the planar honeycomb code by describing boundaries that need no additional physical connectivity, and by optimizing the shape of the qubit patch. We then benchmark the code using Monte Carlo sampling to estimate logical error rates and derive metrics including thresholds, lambdas, and teraquop qubit counts. We determine that the planar honeycomb code can create a logical qubit with one-in-a-trillion logical error rates using 7000 physical qubits at a 0.1% gate-level error rate (or 900 physical qubits given native two-qubit parity measurements). Our results cement the honeycomb code

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13

Li, Xiangrong, and Dafa Li. "Rank-based SLOCC classification for odd $n$ qubits." Quantum Information and Computation 11, no. 7&8 (2011): 695–705. http://dx.doi.org/10.26421/qic11.7-8-10.

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We study the entanglement classification under stochastic local operations and classical communication (SLOCC) for odd n-qubit pure states. For this purpose, we introduce the rank with respect to qubit i for an odd n-qubit state. The ranks with respect to qubits 1,2, ... n give rise to the classification of the space of odd $n$ qubits into 3^n families.

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14

PERDRIX, SIMON. "STATE TRANSFER INSTEAD OF TELEPORTATION IN MEASUREMENT-BASED QUANTUM COMPUTATION." International Journal of Quantum Information 03, no. 01 (2005): 219–23. http://dx.doi.org/10.1142/s0219749905000785.

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Quantum measurement is universal for quantum computation. The model of quantum computation introduced by Nielsen and further developed by Leung relies on a generalized form of teleportation. In order to simulate any n-qubit unitary transformation with this model, four auxiliary qubits are required. Moreover Leung exhibited a universal family of observables composed of one one-qubit measurement and four two-qubit measurements. We introduce a model of quantum computation via measurements only, relying on state transfer: state transfer only retains the part of teleportation which is necessary for

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15

Ben-Aryeh, Y., and A. Mann. "Separability and entanglement of n-qubit and a qubit and a qudit using Hilbert–Schmidt decompositions." International Journal of Quantum Information 14, no. 05 (2016): 1650030. http://dx.doi.org/10.1142/s0219749916500301.

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Hilbert–Schmidt (HS) decompositions are employed for analyzing systems of [Formula: see text]-qubit, and a qubit with a qudit. Negative eigenvalues, obtained by partial-transpose (PT) plus local unitary (PTU) transformations for one qubit from the whole system, are used for indicating entanglement/separability. A sufficient criterion for full separability of the [Formula: see text]-qubit and qubit–qudit systems is given. We use the singular value decomposition (SVD) for improving the criterion for full separability. General properties of entanglement and separability are analyzed for a system

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16

Essammouni, K., A. Chouikh, T. Said, and M. Bennai. "niSWAP and NTCP gates realized in a circuit QED system." International Journal of Geometric Methods in Modern Physics 14, no. 07 (2017): 1750100. http://dx.doi.org/10.1142/s0219887817501006.

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Based on superconducting qubit coupled to a resonator driven by a strong microwave field, we propose a method to implement two quantum logic gates ([Formula: see text]SWAP and NTCP gates) of one qubit simultaneously controlling [Formula: see text] qubits selected from [Formula: see text] qubits in a circuit QED [Formula: see text] by introducing qubit–qubit interaction. The interaction between the qubits and the circuit QED can be achieved by tuning the gate voltage and the external flux. The operation times of the logic gates are much smaller than the decoherence time and dephasing time. More

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17

Sun, Zhi-Hang, Zi-Han Qi, and Peng Xu. "Analysis of the entanglement degree between GHZ and W states under continuous measurement." Laser Physics Letters 22, no. 4 (2025): 045206. https://doi.org/10.1088/1612-202x/adbd20.

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Abstract In most scenarios, particularly when quantum systems are measured to extract information, W states demonstrate greater robustness compared to Greenberger–Horne–Zeilinger (GHZ) states. This study investigates the evolution of entanglement properties in multi-qubit W and GHZ states under continuous measurement. Our findings reveal that, under specific conditions, GHZ states can exhibit superior entanglement properties relative to W states when qubits are measured using a measurement operator. For the three-qubit case, the GHZ state demonstrates stronger entanglement when all three qubit

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18

Herbert, Steven. "On the depth overhead incurred when running quantum algorithms on near-term quantum computers with limited qubit connectivity." Quantum Information and Computation 20, no. 9&10 (2020): 787–806. http://dx.doi.org/10.26421/qic20.9-10-5.

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This paper addresses the problem of finding the depth overhead that will be incurred when running quantum circuits on near-term quantum computers. Specifically, it is envisaged that near-term quantum computers will have low qubit connectivity: each qubit will only be able to interact with a subset of the other qubits, a reality typically represented by a qubit interaction graph in which a vertex represents a qubit and an edge represents a possible direct 2-qubit interaction (gate). Thus the depth overhead is unavoidably incurred by introducing swap gates into the quantum circuit to enable gene

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19

Choi, Jeong Ryeol. "Dynamics of Dispersive Measurements of Flux-Qubit States: Energy-Level Splitting Connected to Quantum Wave Mechanics." Nanomaterials 13, no. 17 (2023): 2395. http://dx.doi.org/10.3390/nano13172395.

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Superconducting flux qubits have many advantages as a storage of quantum information, such as broad range tunability of frequency, small-size fabricability, and high controllability. In the flux qubit–oscillator, qubits are connected to SQUID resonators for the purpose of performing dispersive non-destructive readouts of qubit signals with high fidelity. In this work, we propose a theoretical model for analyzing quantum characteristics of a flux qubit–oscillator on the basis of quantum solutions obtained using a unitary transformation approach. The energy levels of the combined system (qubit +

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20

Solfanelli, Andrea, Alessandro Santini, and Michele Campisi. "Quantum thermodynamic methods to purify a qubit on a quantum processing unit." AVS Quantum Science 4, no. 2 (2022): 026802. http://dx.doi.org/10.1116/5.0091121.

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We report on a quantum thermodynamic method to purify a qubit on a quantum processing unit (QPU) equipped with (nearly) identical qubits. Our starting point is a three qubit design that emulates the well-known two qubit swap engine. Similar to standard fridges, the method would allow us to cool down a qubit at the expense of heating two other qubits. A minimal modification thereof leads to a more practical three qubit design that allows for enhanced refrigeration tasks, such as increasing the purity of one qubit at the expense of decreasing the purity of the other two. The method is based on t

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21

Said, Taoufik, Abdelhaq Chouikh, Karima Essammouni, and Mohamed Bennai. "Realizing an N-two-qubit quantum logic gate in a cavity QED with nearest qubit--qubit interaction." Quantum Information and Computation 16, no. 5&6 (2016): 465–82. http://dx.doi.org/10.26421/qic16.5-6-4.

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We propose an effective way for realizing a three quantum logic gates (NTCP gate, NTCP-NOT gate and NTQ-NOT gate) of one qubit simultaneously controlling N target qubits based on the qubit-qubit interaction. We use the superconducting qubits in a cavity QED driven by a strong microwave field. In our scheme, the operation time of these gates is independent of the number N of qubits involved in the gate operation. These gates are insensitive to the initial state of the cavity QED and can be used to produce an analogous CNOT gate simultaneously acting on N qubits. The quantum phase gate can be re

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Said, T., A. Chouikh, K. Essammouni, and M. Bennai. "Implementing N-quantum phase gate via circuit QED with qubit–qubit interaction." Modern Physics Letters B 30, no. 05 (2016): 1650050. http://dx.doi.org/10.1142/s0217984916500500.

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We propose a method for realizing a quantum phase gate of one qubit simultaneously controlling [Formula: see text] target qubits based on the qubit–qubit interaction. We show how to implement the proposed gate with one transmon qubit simultaneously controlling [Formula: see text] transmon qubits in a circuit QED driven by a strong microwave field. In our scheme, the operation time of this phase gate is independent of the number [Formula: see text] of qubits. On the other hand, this gate can be realized in a time of nanosecond-scale much smaller than the decoherence time and dephasing time both

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23

Чуйкин, О. А., Я. С. Гринберг та А. А. Штыгашев. "Затухание вакуумных осцилляций Раби в двухкубитной структуре в высокодобротном резонаторе". Физика твердого тела 62, № 9 (2020): 1407. http://dx.doi.org/10.21883/ftt.2020.09.49762.13h.

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In this work, we study the damping of vacuum Rabi oscillations for a system of two superconducting solid-state qubits placed in a high-quality microwave resonator. Two different cases are considered: the first qubit is excited at the initial moment, and the initial state is an entangled symmetric and antisymmetric pair. The dependence of the damping on various parameters, primarily on the photon-qubit coupling and on the distance between qubits, is studied in detail. It is shown that for some parameters, the relaxation time of the excited qubit is significantly longer than that for a single qu

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24

Takeda, Kenta, Akito Noiri, Takashi Nakajima, Takashi Kobayashi, and Seigo Tarucha. "Quantum error correction with silicon spin qubits." Nature 608, no. 7924 (2022): 682–86. http://dx.doi.org/10.1038/s41586-022-04986-6.

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AbstractFuture large-scale quantum computers will rely on quantum error correction (QEC) to protect the fragile quantum information during computation1,2. Among the possible candidate platforms for realizing quantum computing devices, the compatibility with mature nanofabrication technologies of silicon-based spin qubits offers promise to overcome the challenges in scaling up device sizes from the prototypes of today to large-scale computers3–5. Recent advances in silicon-based qubits have enabled the implementations of high-quality one-qubit and two-qubit systems6–8. However, the demonstratio

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25

Yuan, Wei-Ping, Zhi-Cheng He, Sai Li, and Zheng-Yuan Xue. "Fast Reset Protocol for Superconducting Transmon Qubits." Applied Sciences 13, no. 2 (2023): 817. http://dx.doi.org/10.3390/app13020817.

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For larger-scale quantum information processing, qubit reset plays an important role, as the coherent times for qubits are limited. However, previous schemes require either long reset times or a complex pulse calibration technique, leading to low efficiency in qubit reset. Here, we propose a fast and simple reset protocol for superconducting transmon qubits based on the coupler-coupled qubits architecture. In this setup, a mixing pulse is used to transfer the qubit excitation to the combined excitation of a low-qulity coupler and readout resonator, which will quickly decay to their respectivel

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26

Jiang, Hanru. "Qubit Recycling Revisited." Proceedings of the ACM on Programming Languages 8, PLDI (2024): 1264–87. http://dx.doi.org/10.1145/3656428.

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Reducing the width of quantum circuits is crucial due to limited number of qubits in quantum devices. This paper revisit an optimization strategy known as qubit recycling (alternatively wire-recycling or measurement-and-reset ), which leverages gate commutativity to reuse discarded qubits, thereby reducing circuit width. We introduce qubit dependency graphs (QDGs) as a key abstraction for this optimization. With QDG, we isolate the computationally demanding components, and observe that qubit recycling is essentially a matrix triangularization problem. Based on QDG and this observation, we stud

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27

MAKHLIN, YU, S. BACKEN, and A. SHNIRMAN. "TWO-QUBIT OPERATION ON MAJORANA QUBITS IN ORDINARY-QUBIT CHAINS." ПИСЬМА В ЖУРНАЛ ЭКСПЕРИМЕНТАЛЬНОЙ И ТЕОРЕТИЧЕСКОЙ ФИЗИКИ 108, no. 11-12 (2018): 779–80. http://dx.doi.org/10.1134/s0370274x1823008x.

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Makhlin, Yu, S. Backens, and A. Shnirman. "Two-Qubit Operation on Majorana Qubits in Ordinary-Qubit Chains." JETP Letters 108, no. 11 (2018): 763–67. http://dx.doi.org/10.1134/s0021364018230029.

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29

Royer, Baptiste, Arne L. Grimsmo, Nicolas Didier, and Alexandre Blais. "Fast and high-fidelity entangling gate through parametrically modulated longitudinal coupling." Quantum 1 (May 11, 2017): 11. http://dx.doi.org/10.22331/q-2017-05-11-11.

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We investigate an approach to universal quantum computation based on the modulation of longitudinal qubit-oscillator coupling. We show how to realize a controlled-phase gate by simultaneously modulating the longitudinal coupling of two qubits to a common oscillator mode. In contrast to the more familiar transversal qubit-oscillator coupling, the magnitude of the effective qubit-qubit interaction does not rely on a small perturbative parameter. As a result, this effective interaction strength can be made large, leading to short gate times and high gate fidelities. We moreover show how the gate

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30

Yirka, Justin, and Yiğit Subaşı. "Qubit-efficient entanglement spectroscopy using qubit resets." Quantum 5 (September 2, 2021): 535. http://dx.doi.org/10.22331/q-2021-09-02-535.

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One strategy to fit larger problems on NISQ devices is to exploit a tradeoff between circuit width and circuit depth. Unfortunately, this tradeoff still limits the size of tractable problems since the increased depth is often not realizable before noise dominates. Here, we develop qubit-efficient quantum algorithms for entanglement spectroscopy which avoid this tradeoff. In particular, we develop algorithms for computing the trace of the n-th power of the density operator of a quantum system, Tr(ρn), (related to the Rényi entropy of order n) that use fewer qubits than any previous efficient al

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Aldeghi, Michele, Rolf Allenspach, and Gian Salis. "Modular nanomagnet design for spin qubits confined in a linear chain." Applied Physics Letters 122, no. 13 (2023): 134003. http://dx.doi.org/10.1063/5.0139670.

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On-chip micromagnets enable electrically controlled quantum gates on electron spin qubits. Extending the concept to a large number of qubits is challenging in terms of providing large enough driving gradients and individual addressability. Here, we present a design aimed at driving spin qubits arranged in a linear chain and strongly confined in directions lateral to the chain. Nanomagnets are placed laterally to the one side of the qubit chain, one nanomagnet per two qubits. The individual magnets are “U”-shaped, such that the magnetic shape anisotropy orients the magnetization alternately tow

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Baßler, Pascal, Matthias Zipper, Christopher Cedzich, et al. "Synthesis of and compilation with time-optimal multi-qubit gates." Quantum 7 (April 20, 2023): 984. http://dx.doi.org/10.22331/q-2023-04-20-984.

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We develop a method to synthesize a class of entangling multi-qubit gates for a quantum computing platform with fixed Ising-type interaction with all-to-all connectivity. The only requirement on the flexibility of the interaction is that it can be switched on and off for individual qubits. Our method yields a time-optimal implementation of the multi-qubit gates. We numerically demonstrate that the total multi-qubit gate time scales approximately linear in the number of qubits. Using this gate synthesis as a subroutine, we provide compilation strategies for important use cases: (i) we show that

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Cai, J. M., Z. W. Zhou, and G. C. Guo. "Fully multi-qubit entangled states." Quantum Information and Computation 7, no. 8 (2007): 766–74. http://dx.doi.org/10.26421/qic7.8-6.

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We investigate the properties of different levels of entanglement in graph states which correspond to connected graphs. Combining the operational definition of graph states and the postulates of entanglement measures, we prove that in connected graph states of $N$ qubits there is no genuine $k$-qubit entanglement, $2\leq k\leq N-1$, among every $k$ qubits. These results about connected graph states naturally lead to the definition of fully multi-qubit entangled states. We also find that the connected graph states of four qubits is one but not the only one class of fully four-qubit entangled st

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Bashkirov, E. K. "Dynamics of a two-qubit Tavis-Cummings model in the presence of an Ising-type interaction between qubits." Computer Optics 48, no. 4 (2024): 475–82. http://dx.doi.org/10.18287/2412-6179-co-1372.

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In this paper, we investigated the dynamics of entanglement of two qubits interacting non-resonantly with the thermal field of a one-mode lossless resonator, taking into account the Ising-type direct interaction between qubits. Based on the exact solution of the quantum Liouville equation, we found the density matrix of the system under consideration. With its help, the reduced qubit-qubit density matrix was calculated and the entanglement criteriоn of the two-qubit system, Pres-Horodeсki parameter, was found. It was shown that for the resonance model and separable initial states of qubits, th

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Javed, Shamiya, Ranjana Prakash, and Hari Prakash. "High success perfect transmission of 1-qubit information using purposefully delayed sharing of non-maximally entangled 2-qubit resource and repeated generalized Bell-state measurements." International Journal of Quantum Information 19, no. 02 (2021): 2150015. http://dx.doi.org/10.1142/s0219749921500155.

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We propose a new scheme in which perfect transmission of 1-qubit information is achieved with high success using purposefully delayed sharing of non-maximally entangled 2-qubit resource and repeated generalized Bell-state measurements (GBSM). Alice possesses initially all qubits and she makes repeated GBSM on the pair of qubits, consisting of (1) the qubit of information state and (2) one of the two entangled resource qubits (taken alternately) until transmission with perfect fidelity is indicated. Alice then sends to Bob, the qubit not used in the last GBSM and also the result of this GBSM an

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Kjaergaard, Morten, Mollie E. Schwartz, Jochen Braumüller, et al. "Superconducting Qubits: Current State of Play." Annual Review of Condensed Matter Physics 11, no. 1 (2020): 369–95. http://dx.doi.org/10.1146/annurev-conmatphys-031119-050605.

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Superconducting qubits are leading candidates in the race to build a quantum computer capable of realizing computations beyond the reach of modern supercomputers. The superconducting qubit modality has been used to demonstrate prototype algorithms in the noisy intermediate-scale quantum (NISQ) technology era, in which non-error-corrected qubits are used to implement quantum simulations and quantum algorithms. With the recent demonstrations of multiple high-fidelity, two-qubit gates as well as operations on logical qubits in extensible superconducting qubit systems, this modality also holds pro

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TAKAHASHI, YASUHIRO. "AN APPROXIMATELY UNIVERSAL SET CONSISTING OF TWO OBSERVABLES." International Journal of Quantum Information 09, no. 06 (2011): 1393–412. http://dx.doi.org/10.1142/s021974991100809x.

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We consider the problem of minimizing the resources required for approximate universality in measurement-only quantum computation. This problem is important not only for realizing a quantum computer, but also for understanding the computational power of quantum computation. The resources we focus on are observables, which describe projective measurements, and ancillary qubits. We show that, if we are allowed to use two ancillary qubits, the set of observables { cos (π/8)X - sin (π/8)Y ,Z ⊗ X} is approximately universal for quantum computation. This is the first construction of an approximately

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Sánchez-Burillo, Eduardo, Juanjo García-Ripoll, Luis Martín-Moreno, and David Zueco. "Nonlinear quantum optics in the (ultra)strong light–matter coupling." Faraday Discussions 178 (2015): 335–56. http://dx.doi.org/10.1039/c4fd00206g.

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The propagation of N photons in one dimensional waveguides coupled to M qubits is discussed, both in the strong and ultrastrong qubit–waveguide coupling. Special emphasis is placed on the characterisation of the nonlinear response and its linear limit for the scattered photons as a function of N, M, qubit inter distance and light–matter coupling. The quantum evolution is numerically solved via the matrix product states technique. The time evolutions for both the field and qubits are computed. The nonlinear character (as a function of N/M) depends on the computed observable. While perfect refle

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Bagrov, Alexander R., and Eugene K. Bashkirov. "Dynamics of qubit entanglement in three-qubit Jaynes–Cummings model for biseparable intial states." Physics of Wave Processes and Radio Systems 27, no. 4 (2024): 7–19. https://doi.org/10.18469/1810-3189.2024.27.4.7-19.

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Background. To operate a quantum computer, a set of universal gates must be implemented, such as a two-cubit gate of the controlled negation type plus one-cubit spins. As a universal alternative, three-cubic-bit gates may be used. In this regard, it seems very relevant to investigate the dynamics of three-qubit systems in microwave resonators, in particular to study the most efficient schemes for generating, controlling, and monitoring entangled qubit states. Aim. To investigate the features of the dynamics of entangled pairs of qubits for a system in which two qubits are locked in a single-mo

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Xue, Xiao, Maximilian Russ, Nodar Samkharadze, et al. "Quantum logic with spin qubits crossing the surface code threshold." Nature 601, no. 7893 (2022): 343–47. http://dx.doi.org/10.1038/s41586-021-04273-w.

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AbstractHigh-fidelity control of quantum bits is paramount for the reliable execution of quantum algorithms and for achieving fault tolerance—the ability to correct errors faster than they occur1. The central requirement for fault tolerance is expressed in terms of an error threshold. Whereas the actual threshold depends on many details, a common target is the approximately 1% error threshold of the well-known surface code2,3. Reaching two-qubit gate fidelities above 99% has been a long-standing major goal for semiconductor spin qubits. These qubits are promising for scaling, as they can lever

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Tang, Haotian, Fei Ding, Xueyun Cheng, Shuxian Zhao, and Zhijin Guan. "Width Optimization of Quantum Circuit Based on Reuse-Aimed Quantum Circuit Transformation." Quantum Information & Computation 25, no. 3 (2025): 216–31. https://doi.org/10.2478/qic-2025-0011.

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Abstract Due to constraints in current quantum hardware manufacturing, the number of available qubits remains limited. This limitation poses significant challenges to the feasibility of quantum computation. Qubit reuse, supported by the hardware-enabled dynamic quantum circuit, has emerged as a promising method for optimizing the width of quantum circuits. However, enabling width optimization through qubit reuse for circuits that lack qubit reuse opportunities remains a challenging problem. This paper aims to address this challenge by introducing RaQCT (Reuseaimed Quantum Circuit Transformatio

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Gennaro, Giuseppe. "Relaxation Due to the Partial Swap Collisions with a Random Reservoir." Open Systems & Information Dynamics 18, no. 04 (2011): 353–62. http://dx.doi.org/10.1142/s1230161211000248.

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We analyze the dynamics of the system consisting of a qubit sequentially interacting with a chain of qubits that are initially individually in a pure random state. Each pairwise collision has been modeled as a partial swap transformation. The relaxation to equilibrium of the purity of the system qubit, averaged over all the initial states of the environment, is analytically computed. In particular, we show that the steady state depends on the parameter η of the partial swap transformation. Finally, we investigate aspects of the entanglement dynamics for qubits and show that such process can cr

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FUJII, TOSHIYUKI, MUNEHIRO NISHIDA, SATOSHI TANDA, and NORIYUKI HATAKENAKA. "TALKING BREATHER QUBITS." International Journal of Modern Physics B 23, no. 20n21 (2009): 4352–64. http://dx.doi.org/10.1142/s0217979209063511.

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Breather is an elementary excitation regarded as a bound state of a fluxon and an antifluxon in a long Josephson junction. In quantum-mechanical regime, the breather energy is quantized so that the breather can be considered as an artificial moving atom. We propose a new type of fluxon qubit that is constructed by quantum-mechanical superposition of the breather's states. We describe quantum logic gates of breather qubit required for constructing quantum computer. In addition, our qubit can move in the system so that transfer of quntum information is possible between mobile qubits as well as s

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Chao, Rui, Michael E. Beverland, Nicolas Delfosse, and Jeongwan Haah. "Optimization of the surface code design for Majorana-based qubits." Quantum 4 (October 28, 2020): 352. http://dx.doi.org/10.22331/q-2020-10-28-352.

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The surface code is a prominent topological error-correcting code exhibiting high fault-tolerance accuracy thresholds. Conventional schemes for error correction with the surface code place qubits on a planar grid and assume native CNOT gates between the data qubits with nearest-neighbor ancilla qubits.Here, we present surface code error-correction schemes using only Pauli measurements on single qubits and on pairs of nearest-neighbor qubits. In particular, we provide several qubit layouts that offer favorable trade-offs between qubit overhead, circuit depth and connectivity degree. We also dev

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XU, PENG, LIE WU, and NIAN-QUAN JIANG. "REALIZATION OF 1 → n CONTROLLED PHASE GATE IN CAVITY QED." International Journal of Quantum Information 09, no. 02 (2011): 773–78. http://dx.doi.org/10.1142/s021974991100771x.

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A scheme for realizing a multi-qubit phase gate with one control qubit simultaneously controlling n target qubits in a cavity QED system is proposed. The operation time of the gate is independent of the number n of qubits. The realizability of the gate with current technology is also discussed.

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Kumar, Preethika, and Steven R. Skinner. "Universal quantum computing in linear nearest neighbor architectures." Quantum Information and Computation 11, no. 3&4 (2011): 300–312. http://dx.doi.org/10.26421/qic11.3-4-8.

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We introduce a scheme for realizing universal quantum computing in a linear nearest neighbor architecture with fixed couplings. We first show how to realize a controlled-NOT gate operation between two adjacent qubits without having to isolate the two qubits from qubits adjacent to them. The gate operation is implemented by applying two consecutive pulses of equal duration, but varying amplitudes, on the target qubit. Since only a single control parameter is required in implementing our scheme, it is very efficient. We next show how our scheme can be used to realize single qubit rotations and t

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Xu, Yilun, Gang Huang, Jan Balewski, et al. "Automatic Qubit Characterization and Gate Optimization with QubiC." ACM Transactions on Quantum Computing, April 13, 2022. http://dx.doi.org/10.1145/3529397.

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As the size and complexity of a quantum computer increases, quantum bit (qubit) characterization and gate optimization become complex and time-consuming tasks. Current calibration techniques require complicated and verbose measurements to tune up qubits and gates, which cannot easily expand to the large-scale quantum systems. We develop a concise and automatic calibration protocol to characterize qubits and optimize gates using QubiC , which is an open source FPGA (field-programmable gate array) based control and measurement system for superconducting quantum information processors. We propose

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Joo, Jaewoo, Chang-Woo Lee, Shingo Kono, and Jaewan Kim. "Logical measurement-based quantum computation in circuit-QED." Scientific Reports 9, no. 1 (2019). http://dx.doi.org/10.1038/s41598-019-52866-3.

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Abstract We propose a new scheme of measurement-based quantum computation (MBQC) using an error-correcting code against photon-loss in circuit quantum electrodynamics. We describe a specific protocol of logical single-qubit gates given by sequential cavity measurements for logical MBQC and a generalised Schrödinger cat state is used for a continuous-variable (CV) logical qubit captured in a microwave cavity. To apply an error-correcting scheme on the logical qubit, we utilise a d-dimensional quantum system called a qudit. It is assumed that a three CV-qudit entangled state is initially prepare

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Delteil, Aymeric. "N-qubit universal quantum logic with a photonic qudit and O(N) linear optics elements." APL Quantum 1, no. 4 (2024). http://dx.doi.org/10.1063/5.0223431.

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High-dimensional quantum units of information, or qudits, can carry more than one quantum bit of information in a single degree of freedom and can, therefore, be used to boost the performance of quantum communication and quantum computation protocols. A photon in a superposition of 2N time bins—a time-bin qudit—contains as much information as N qubits. Here, we show that N-qubit states encoded in a single time-bin qudit can be arbitrarily and deterministically generated, manipulated, and measured using a number of linear optics elements that scale linearly with N, as opposed to prior proposals

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Miyahara, Hideyuki, Yiyou Chen, Vwani Roychowdhury, and Louis-Serge Bouchard. "Decoherence mitigation by embedding a logical qubit in a qudit." Quantum Information Processing 22, no. 7 (2023). http://dx.doi.org/10.1007/s11128-023-04035-9.

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AbstractQuantum information stored in a qubit is rapidly lost to the environment. The realization of robust qubits is one of the most important challenges in quantum computing. Herein, we propose to embed a logical qubit within the manifold of a qudit as a scheme to preserve quantum information over extended periods of time. Under identical conditions (e.g., decoherence channels), the submanifold of the logical qubit exhibits extended lifetimes compared to a pure two-level system (qubit). The retention of quantum information further improves with separation between the sublevels of the logical

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