Journal articles: 'Multi-qubit quantum gates'

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Baßler, Pascal, Markus Heinrich, and Martin Kliesch. "Time-optimal multi-qubit gates: Complexity, efficient heuristic and gate-time bounds." Quantum 8 (March 13, 2024): 1279. http://dx.doi.org/10.22331/q-2024-03-13-1279.

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Multi-qubit entangling interactions arise naturally in several quantum computing platforms and promise advantages over traditional two-qubit gates. In particular, a fixed multi-qubit Ising-type interaction together with single-qubit X-gates can be used to synthesize global ZZ-gates (GZZ gates). In this work, we first show that the synthesis of such quantum gates that are time-optimal is NP-hard. Second, we provide explicit constructions of special time-optimal multi-qubit gates. They have constant gate times and can be implemented with linearly many X-gate layers. Third, we develop a heuristic algorithm with polynomial runtime for synthesizing fast multi-qubit gates. Fourth, we derive lower and upper bounds on the optimal GZZ gate-time. Based on explicit constructions of GZZ gates and numerical studies, we conjecture that any GZZ gate can be executed in a time O(n) for n qubits. Our heuristic synthesis algorithm leads to GZZ gate-times with a similar scaling, which is optimal in this sense. We expect that our efficient synthesis of fast multi-qubit gates allows for faster and, hence, also more error-robust execution of quantum algorithms.

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HEYDARI, HOSHANG. "GENERALIZED CONTROLLED PHASE QUANTUM GATES ENTANGLERS." International Journal of Quantum Information 07, no. 06 (September 2009): 1211–16. http://dx.doi.org/10.1142/s021974990900581x.

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We construct a generalized controlled phased gate entangler for a multi-qubit state based on the geometrical structure of quantum systems. We also investigate the relation between the generalized controlled phase construction of a quantum gate entangler and graph state for two-qubit and three-qubit states.

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Atiya, Abdulkader H., and Mohammed Al-Temimi. "Review of Recent Laser Technology of Development Multi Qubit Gates Using Ion Trap Method." Applied Mechanics and Materials 915 (August 18, 2023): 33–42. http://dx.doi.org/10.4028/p-j6vsf9.

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The qubit technology using Trapped ions are taking the systems for practical quantum computing (QC). The normal requirements to achieve quantum supremacy have all been studied with ions, and quantum algorithms use ion-qubit systems have been implemented. I cover in this study many points regarding the concept of Qubit through Ion Trap, near application, and experiments also explore the Multi gates, Hybrid gates implementations

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Sun, Shiya, and Huisheng Zhang. "Deterministic quantum cyclic controlled teleportation of arbitrary multi-qubit states using multi-qubit partially entangled channel." Modern Physics Letters A 35, no. 25 (June 30, 2020): 2050204. http://dx.doi.org/10.1142/s0217732320502041.

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In this paper, we present a deterministic four-party quantum cyclic controlled teleportation (QCYCT) scheme, by using a multi-qubit partially entangled state as the quantum channel. In this scheme, Alice can teleport an arbitrary [Formula: see text]-qubit state to Bob, Bob can teleport an arbitrary [Formula: see text]-qubit state to Charlie and Charlie can teleport an arbitrary [Formula: see text]-qubit state to Alice under the control of the supervisor David. We utilize rotation gate, Hadamard gates and controlled-NOT (CNOT) gates to construct the multi-qubit partially entangled channel. Only Bell-state measurements, single-qubit von-Neumann measurement and proper unitary operations are required in this scheme, which can be realized in practice easily based on the present quantum experiment technologies. The direction of cyclic controlled teleportation of arbitrary multi-qubit states can also be changed by altering the quantum channel. Analysis demonstrates that the success probability of the proposed scheme can still reach 100% although the quantum channel is non-maximally entangled. Furthermore, the proposed four-party scheme can be generalized into the case involving [Formula: see text] correspondents, which is more suitable for quantum communication networks. We also calculate the intrinsic efficiency and discuss the security of the proposed scheme. Compared with the existing QCYCT schemes which realized cyclic controlled teleportation of arbitrary single-qubit states, specific two-qubit and three-qubit states, the proposed scheme is of general significance.

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Gao, Xiaoqin, Paul Appel, Nicolai Friis, Martin Ringbauer, and Marcus Huber. "On the role of entanglement in qudit-based circuit compression." Quantum 7 (October 16, 2023): 1141. http://dx.doi.org/10.22331/q-2023-10-16-1141.

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Gate-based universal quantum computation is formulated in terms of two types of operations: local single-qubit gates, which are typically easily implementable, and two-qubit entangling gates, whose faithful implementation remains one of the major experimental challenges since it requires controlled interactions between individual systems. To make the most of quantum hardware it is crucial to process information in the most efficient way. One promising avenue is to use higher-dimensional systems, qudits, as the fundamental units of quantum information, in order to replace a fraction of the qubit-entangling gates with qudit-local gates. Here, we show how the complexity of multi-qubit circuits can be lowered significantly by employing qudit encodings, which we quantify by considering exemplary circuits with exactly known (multi-qubit) gate complexity. We discuss general principles for circuit compression, derive upper and lower bounds on the achievable advantage, and highlight the key role played by entanglement and the available gate set. Explicit experimental schemes for photonic as well as for trapped-ion implementations are provided and demonstrate a significant expected gain in circuit performance for both platforms.

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Baßler, Pascal, Matthias Zipper, Christopher Cedzich, Markus Heinrich, Patrick H. Huber, Michael Johanning, and Martin Kliesch. "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 any Clifford circuit on n qubits can be implemented using at most 2n multi-qubit gates without requiring ancilla qubits, (ii) we decompose the quantum Fourier transform in a similar fashion, (iii) we compile a simulation of molecular dynamics, and (iv) we propose a method for the compilation of diagonal unitaries with time-optimal multi-qubit gates, as a step towards general unitaries. As motivation, we provide a detailed discussion on a microwave controlled ion trap architecture with magnetic gradient induced coupling (MAGIC) for the generation of the Ising-type interactions.

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Stas, P. J., Y. Q. Huan, B. Machielse, E. N. Knall, A. Suleymanzade, B. Pingault, M. Sutula, et al. "Robust multi-qubit quantum network node with integrated error detection." Science 378, no. 6619 (November 4, 2022): 557–60. http://dx.doi.org/10.1126/science.add9771.

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Long-distance quantum communication and networking require quantum memory nodes with efficient optical interfaces and long memory times. We report the realization of an integrated two-qubit network node based on silicon-vacancy centers (SiVs) in diamond nanophotonic cavities. Our qubit register consists of the SiV electron spin acting as a communication qubit and the strongly coupled silicon-29 nuclear spin acting as a memory qubit with a quantum memory time exceeding 2 seconds. By using a highly strained SiV, we realize electron-photon entangling gates at temperatures up to 1.5 kelvin and nucleus-photon entangling gates up to 4.3 kelvin. We also demonstrate efficient error detection in nuclear spin–photon gates by using the electron spin as a flag qubit, making this platform a promising candidate for scalable quantum repeaters.

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Litinski, Daniel, and Felix von Oppen. "Lattice Surgery with a Twist: Simplifying Clifford Gates of Surface Codes." Quantum 2 (May 4, 2018): 62. http://dx.doi.org/10.22331/q-2018-05-04-62.

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We present a planar surface-code-based scheme for fault-tolerant quantum computation which eliminates the time overhead of single-qubit Clifford gates, and implements long-range multi-target CNOT gates with a time overhead that scales only logarithmically with the control-target separation. This is done by replacing hardware operations for single-qubit Clifford gates with a classical tracking protocol. Inter-qubit communication is added via a modified lattice surgery protocol that employs twist defects of the surface code. The long-range multi-target CNOT gates facilitate magic state distillation, which renders our scheme fault-tolerant and universal.

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Urías, Jesús, and Diego A. Quiñones. "Householder methods for quantum circuit design." Canadian Journal of Physics 94, no. 2 (February 2016): 150–57. http://dx.doi.org/10.1139/cjp-2015-0490.

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Algorithms to resolve multiple-qubit unitary transformations into a sequence of simple operations on one-qubit subsystems are central to the methods of quantum-circuit simulators. We adapt Householder’s theorem to the tensor-product character of multi-qubit state vectors and translate it to a combinatorial procedure to assemble cascades of quantum gates that recreate any unitary operation U acting on n-qubit systems. U may be recreated by any cascade from a set of combinatorial options that, in number, are not lesser than super-factorial of 2n, [Formula: see text]. Cascades are assembled with one-qubit controlled-gates of a single type. We complement the assembly procedure with a new algorithm to generate Gray codes that reduce the combinatorial options to cascades with the least number of CNOT gates. The combined procedure —factorization, gate assembling, and Gray ordering — is illustrated on an array of three qubits.

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Ufrecht, Christian, Maniraman Periyasamy, Sebastian Rietsch, Daniel D. Scherer, Axel Plinge, and Christopher Mutschler. "Cutting multi-control quantum gates with ZX calculus." Quantum 7 (October 23, 2023): 1147. http://dx.doi.org/10.22331/q-2023-10-23-1147.

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Circuit cutting, the decomposition of a quantum circuit into independent partitions, has become a promising avenue towards experiments with larger quantum circuits in the noisy-intermediate scale quantum (NISQ) era. While previous work focused on cutting qubit wires or two-qubit gates, in this work we introduce a method for cutting multi-controlled Z gates. We construct a decomposition and prove the upper bound O(62K) on the associated sampling overhead, where K is the number of cuts in the circuit. This bound is independent of the number of control qubits but can be further reduced to O(4.52K) for the special case of CCZ gates. Furthermore, we evaluate our proposal on IBM hardware and experimentally show noise resilience due to the strong reduction of CNOT gates in the cut circuits.

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11

Heydari, Hoshang. "Selective Phase Rotation Quantum Gate Entangler." Open Systems & Information Dynamics 16, no. 04 (December 2009): 407–12. http://dx.doi.org/10.1142/s1230161209000293.

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We construct a quantum gate entangler for multi-qubit states based on a selective phase rotation transform. In particular, we establish a relation between the quantum integral transform and the quantum gate entangler in terms of universal controlled gates for multi-qubit states. Our result gives an effective way of constructing topological and geometrical quantum gate entanglers for multipartite quantum systems, which could also lead to a construction of geometrical quantum algorithms.

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12

Seddon, James R., and Earl T. Campbell. "Quantifying magic for multi-qubit operations." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, no. 2227 (July 2019): 20190251. http://dx.doi.org/10.1098/rspa.2019.0251.

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The development of a framework for quantifying ‘non-stabilizerness’ of quantum operations is motivated by the magic state model of fault-tolerant quantum computation and by the need to estimate classical simulation cost for noisy intermediate-scale quantum (NISQ) devices. The robustness of magic was recently proposed as a well-behaved magic monotone for multi-qubit states and quantifies the simulation overhead of circuits composed of Clifford + T gates, or circuits using other gates from the Clifford hierarchy. Here we present a general theory of the ‘non-stabilizerness’ of quantum operations rather than states, which are useful for classical simulation of more general circuits. We introduce two magic monotones, called channel robustness and magic capacity, which are well-defined for general n -qubit channels and treat all stabilizer-preserving CPTP maps as free operations. We present two complementary Monte Carlo-type classical simulation algorithms with sample complexity given by these quantities and provide examples of channels where the complexity of our algorithms is exponentially better than previously known simulators. We present additional techniques that ease the difficulty of calculating our monotones for special classes of channels.

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Innocenti, Luca, Leonardo Banchi, Sougato Bose, Alessandro Ferraro, and Mauro Paternostro. "Approximate supervised learning of quantum gates via ancillary qubits." International Journal of Quantum Information 16, no. 08 (December 2018): 1840004. http://dx.doi.org/10.1142/s021974991840004x.

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We present strategies for the training of a qubit network aimed at the ancilla-assisted synthesis of multi-qubit gates based on a set of restricted resources. By assuming the availability of only time-independent single and two-qubit interactions, we introduce and describe a supervised learning strategy implemented through momentum-stochastic gradient descent with automatic differentiation methods. We demonstrate the effectiveness of the scheme by discussing the implementation of nontrivial three qubit operations, including a QFT and a half-adder gate.

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14

Jones, Cody. "Distillation protocols for Fourier states in quantum computing." Quantum Information and Computation 14, no. 7&8 (May 2014): 560–76. http://dx.doi.org/10.26421/qic14.7-8-2.

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Fourier states are multi-qubit registers that facilitate phase rotations in fault-tolerant quantum computing. We propose distillation protocols for constructing the fundamental, $n$-qubit Fourier state with error $O(2^{-n})$ at a cost of $O(n \log n)$ Toffoli gates and Clifford gates, or any arbitrary Fourier state using $O(n^2)$ gates. We analyze these protocols with methods from digital signal processing. These results suggest that phase kickback, which uses Fourier states, could be the current lowest-overhead method for generating arbitrary phase rotations.

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15

Spiteri, Raymond J., Marina Schmidt, Joydip Ghosh, Ehsan Zahedinejad, and Barry C. Sanders. "Quantum control for high-fidelity multi-qubit gates." New Journal of Physics 20, no. 11 (November 15, 2018): 113009. http://dx.doi.org/10.1088/1367-2630/aae79a.

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16

Wang, Dong. "Remote Implementation of Multi-qubit Quantum Phase Gates." International Journal of Theoretical Physics 49, no. 4 (January 30, 2010): 777–85. http://dx.doi.org/10.1007/s10773-010-0257-x.

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Dai, J., and R. V. Krems. "Quantum Gaussian process model of potential energy surface for a polyatomic molecule." Journal of Chemical Physics 156, no. 18 (May 14, 2022): 184802. http://dx.doi.org/10.1063/5.0088821.

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With gates of a quantum computer designed to encode multi-dimensional vectors, projections of quantum computer states onto specific qubit states can produce kernels of reproducing kernel Hilbert spaces. We show that quantum kernels obtained with a fixed ansatz implementable on current quantum computers can be used for accurate regression models of global potential energy surfaces (PESs) for polyatomic molecules. To obtain accurate regression models, we apply Bayesian optimization to maximize marginal likelihood by varying the parameters of the quantum gates. This yields Gaussian process models with quantum kernels. We illustrate the effect of qubit entanglement in the quantum kernels and explore the generalization performance of quantum Gaussian processes by extrapolating global six-dimensional PESs in the energy domain.

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Algaba, Manuel G., P. V. Sriluckshmy, Martin Leib, and Fedor Šimkovic IV. "Low-depth simulations of fermionic systems on square-grid quantum hardware." Quantum 8 (April 30, 2024): 1327. http://dx.doi.org/10.22331/q-2024-04-30-1327.

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We present a general strategy for mapping fermionic systems to quantum hardware with square qubit connectivity which yields low-depth quantum circuits, counted in the number of native two-qubit fSIM gates. We achieve this by leveraging novel operator decomposition and circuit compression techniques paired with specifically chosen low-depth fermion-to-qubit mappings and allow for a high degree of gate cancellations and parallelism. Our mappings retain the flexibility to simultaneously optimize for qubit counts or qubit operator weights and can be used to investigate arbitrary fermionic lattice geometries. We showcase our approach by investigating the tight-binding model, the Fermi-Hubbard model as well as the multi-orbital Hubbard-Kanamori model. We report unprecedentedly low circuit depths per single Trotter layer with up to a 70% improvement upon previous state-of-the-art. Our compression technique also results in significant reduction of two-qubit gates. We find the lowest gate-counts when applying the XYZ-formalism to the DK mapping. Additionally, we show that our decomposition and compression formalism produces favourable circuits even when no native parameterized two-qubit gates are available.

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Huang, Keli, and Jens Palsberg. "Compiling Conditional Quantum Gates without Using Helper Qubits." Proceedings of the ACM on Programming Languages 8, PLDI (June 20, 2024): 1463–84. http://dx.doi.org/10.1145/3656436.

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We present a compilation scheme for conditional quantum gates. Our scheme compiles a multi-qubit conditional to a linear number of two-qubit conditionals. This can be done straightforwardly with helper qubits, but we show how to do it without using helper qubits and with much fewer gates than in previous work. Specifically, our scheme requires 1/3 as many gates as the previous best scheme without using helper qubits, which is essential for practical use. Our experiments show that several quantum-circuit optimizers have little impact on the compiled code from the previous best scheme, confirming the need for our new scheme. Our experiments with Grover's algorithm and quantum walk also show that our scheme has a major impact on the reliability of the compiled code.

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Li, Panchi, Jiahui Guo, Bing Wang, and Mengqi Hao. "Quantum circuits for calculating the squared sum of the inner product of quantum states and its application." International Journal of Quantum Information 17, no. 05 (August 2019): 1950043. http://dx.doi.org/10.1142/s0219749919500436.

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In this paper, we propose a quantum circuit for calculating the squared sum of the inner product of quantum states. The circuit is designed by the multi-qubits controlled-swapping gates, in which the initial state of each control qubit is [Formula: see text] and they are in the equilibrium superposition state after passing through some Hadamard gates. Then, according to the control rules, each basis state in the superposition state controls the corresponding quantum states pair to swap. Finally, the Hadamard gates are applied to the control qubits again, and the squared sum of the inner product of many pairs of quantum states can be obtained simultaneously by measuring only one control qubit. We investigate the application of this method in quantum images matching on a classical computer, and the experimental results verify the correctness of the proposed method.

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Dawson, C. M., and M. A. Nielsen. "The Solovay-Kitaev algorithm." Quantum Information and Computation 6, no. 1 (January 2006): 81–95. http://dx.doi.org/10.26421/qic6.1-6.

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This pedagogical review presents the proof of the Solovay-Kitaev theorem in the form of an efficient classical algorithm for compiling an arbitrary single-qubit gate into a sequence of gates from a fixed and finite set. The algorithm can be used, for example, to compile Shor's algorithm, which uses rotations of $\pi / 2^k$, into an efficient fault-tolerant form using only Hadamard, controlled-{\sc not}, and $\pi / 8$ gates. The algorithm runs in $O(\log^{2.71}(1/\epsilon))$ time, and produces as output a sequence of $O(\log^{3.97}(1/\epsilon))$ quantum gates which is guaranteed to approximate the desired quantum gate to an accuracy within $\epsilon > 0$. We also explain how the algorithm can be generalized to apply to multi-qubit gates and to gates from SU(d).

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Marbaniang, Leniency, and Kamalika Datta. "Efficient Design of Quantum Circuits Using Nearest Neighbor Constraint in 3D Architecture." Journal of Circuits, Systems and Computers 28, no. 05 (May 2019): 1950084. http://dx.doi.org/10.1142/s0218126619500841.

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Synthesis and optimization of quantum circuits have received significant attention from researchers in recent years. Developments in the physical realization of qubits in quantum computing have led to new physical constraints to be addressed. One of the most important constraints that is considered by many researchers is the nearest neighbor constraint which limits the interaction distance between qubits for quantum gate operations. Various works have been reported in the literature that deal with nearest neighbor compliance in multi-dimensional (mostly 1D and 2D) qubit arrangements. This is normally achieved by inserting SWAP gates in the gate netlist to bring the interacting qubits closer together. The main objective function to minimize here is the number of SWAP gates. The present paper proposes an efficient qubit placement strategy in a three-dimensional (3D) grid that considers not only qubit interactions but also the relative positions of the gates in the circuit. Experimental evaluation on a number of benchmark circuits show that the proposed method reduces the number of SWAP gates by 16.2% to 47.0% on the average as compared to recently published works.

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23

Sriluckshmy, P. V., Vicente Pina-Canelles, Mario Ponce, Manuel G. Algaba, Fedor Šimkovic IV, and Martin Leib. "Optimal, hardware native decomposition of parameterized multi-qubit Pauli gates." Quantum Science and Technology 8, no. 4 (September 25, 2023): 045029. http://dx.doi.org/10.1088/2058-9565/acfa20.

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Abstract We show how to efficiently decompose a parameterized multi-qubit Pauli (PMQP) gate into native parameterized two-qubit Pauli (P2QP) gates minimizing both the circuit depth and the number of P2QP gates. Given a realistic quantum computational model, we argue that the technique is optimal in terms of the number of hardware native gates and the overall depth of the decomposition. Starting from PMQP gate decompositions for the path and star hardware graph, we generalize the procedure to any generic hardware graph and provide exact expressions for the depth and number of P2QP gates of the decomposition. Furthermore, we show how to efficiently combine the decomposition of multiple PMQP gates to further reduce the depth as well as the number of P2QP gates for a combinatorial optimization problem using the Lechner–Hauke–Zoller mapping.

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Bhattacharyya, Shaman, and Somnath Bhattacharyya. "Demonstration of the Holonomically Controlled Non-Abelian Geometric Phase in a Three-Qubit System of a Nitrogen Vacancy Center." Entropy 24, no. 11 (November 2, 2022): 1593. http://dx.doi.org/10.3390/e24111593.

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The holonomic approach to controlling (nitrogen-vacancy) NV-center qubits provides an elegant way of theoretically devising universal quantum gates that operate on qubits via calculable microwave pulses. There is, however, a lack of simulated results from the theory of holonomic control of quantum registers with more than two qubits describing the transition between the dark states. Considering this, we have been experimenting with the IBM Quantum Experience technology to determine the capabilities of simulating holonomic control of NV-centers for three qubits describing an eight-level system that produces a non-Abelian geometric phase. The tunability of the geometric phase via the detuning frequency is demonstrated through the high fidelity (~85%) of three-qubit off-resonant holonomic gates over the on-resonant ones. The transition between the dark states shows the alignment of the gate’s dark state with the qubit’s initial state hence decoherence of the multi-qubit system is well-controlled through a π/3 rotation.

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Martinez, Esteban A., Thomas Monz, Daniel Nigg, Philipp Schindler, and Rainer Blatt. "Compiling quantum algorithms for architectures with multi-qubit gates." New Journal of Physics 18, no. 6 (June 24, 2016): 063029. http://dx.doi.org/10.1088/1367-2630/18/6/063029.

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Ellinas, Demosthenes. "Operational Algorithms for Separable Qubit X States." Condensed Matter 4, no. 3 (July 2, 2019): 64. http://dx.doi.org/10.3390/condmat4030064.

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This work motivates and applies operational methodology to simulation of quantum statistics of separable qubit X states. Three operational algorithms for evaluating separability probability distributions are put forward. Building on previous findings, the volume function characterizing the separability distribution is determined via quantum measurements of multi-qubit observables. Three measuring states, one for each algorithm are generated via (i) a multi-qubit channel map, (ii) a unitary operator generated by a Hamiltonian describing a non-uniform hypergraph configuration of interactions among 12 qubits, and (iii) a quantum walk CP map in a extended state space. Higher order CZ gates are the only tools of the algorithms hence the work associates itself computationally with the Instantaneous Quantum Polynomial-time Circuits (IQP), while wrt possible implementation the work relates to the Lechner-Hauke-Zoller (LHZ) architecture of higher order coupling. Finally some uncertainty aspects of the quantum measurement observables are discussed together with possible extensions to non-qubit separable bipartite systems.

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Allcock, Jonathan, Jinge Bao, Joao F. Doriguello, Alessandro Luongo, and Miklos Santha. "Constant-depth circuits for Boolean functions and quantum memory devices using multi-qubit gates." Quantum 8 (November 20, 2024): 1530. http://dx.doi.org/10.22331/q-2024-11-20-1530.

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We explore the power of the unbounded Fan-Out gate and the Global Tunable gates generated by Ising-type Hamiltonians in constructing constant-depth quantum circuits, with particular attention to quantum memory devices. We propose two types of constant-depth constructions for implementing Uniformly Controlled Gates. These gates include the Fan-In gates defined by |x⟩|b⟩↦|x⟩|b⊕f(x)⟩ for x∈{0,1}n and b∈{0,1}, where f is a Boolean function. The first of our constructions is based on computing the one-hot encoding of the control register |x⟩, while the second is based on Boolean analysis and exploits different representations of f such as its Fourier expansion. Via these constructions, we obtain constant-depth circuits for the quantum counterparts of read-only and read-write memory devices – Quantum Random Access Memory (QRAM) and Quantum Random Access Gate (QRAG) – of memory size n. The implementation based on one-hot encoding requires either O(nlog(d)⁡nlog(d+1)⁡n) ancillae and O(nlog(d)⁡n) Fan-Out gates or O(nlog(d)⁡n) ancillae and 16d−10 Global Tunable gates, where d is any positive integer and log(d)⁡n=log⁡⋯log⁡n is the d-times iterated logarithm. On the other hand, the implementation based on Boolean analysis requires 8d−6 Global Tunable gates at the expense of O(n1/(1−2−d)) ancillae.

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Raveh, David, and Rafael I. Nepomechie. "Deterministic Bethe state preparation." Quantum 8 (October 24, 2024): 1510. http://dx.doi.org/10.22331/q-2024-10-24-1510.

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We present an explicit quantum circuit that prepares an arbitrary U(1)-eigenstate on a quantum computer, including the exact eigenstates of the spin-1/2XXZ quantum spin chain with either open or closed boundary conditions. The algorithm is deterministic, does not require ancillary qubits, and does not require QR decompositions. The circuit prepares such an L-qubit state with M down-spins using (LM)−1 multi-controlled rotation gates and 2M(L−M) CNOT-gates.

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Wu, Bujiao, Xiaoyang Wang, Xiao Yuan, Cupjin Huang, and Jianxin Chen. "Leakage Benchmarking for Universal Gate Sets." Entropy 26, no. 1 (January 13, 2024): 71. http://dx.doi.org/10.3390/e26010071.

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Errors are common issues in quantum computing platforms, among which leakage is one of the most-challenging to address. This is because leakage, i.e., the loss of information stored in the computational subspace to undesired subspaces in a larger Hilbert space, is more difficult to detect and correct than errors that preserve the computational subspace. As a result, leakage presents a significant obstacle to the development of fault-tolerant quantum computation. In this paper, we propose an efficient and accurate benchmarking framework called leakage randomized benchmarking (LRB), for measuring leakage rates on multi-qubit quantum systems. Our approach is more insensitive to state preparation and measurement (SPAM) noise than existing leakage benchmarking protocols, requires fewer assumptions about the gate set itself, and can be used to benchmark multi-qubit leakages, which has not been achieved previously. We also extended the LRB protocol to an interleaved variant called interleaved LRB (iLRB), which can benchmark the average leakage rate of generic n-site quantum gates with reasonable noise assumptions. We demonstrate the iLRB protocol on benchmarking generic two-qubit gates realized using flux tuning and analyzed the behavior of iLRB under corresponding leakage models. Our numerical experiments showed good agreement with the theoretical estimations, indicating the feasibility of both the LRB and iLRB protocols.

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Pérez-Salinas, Adrián, Alba Cervera-Lierta, Elies Gil-Fuster, and José I. Latorre. "Data re-uploading for a universal quantum classifier." Quantum 4 (February 6, 2020): 226. http://dx.doi.org/10.22331/q-2020-02-06-226.

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A single qubit provides sufficient computational capabilities to construct a universal quantum classifier when assisted with a classical subroutine. This fact may be surprising since a single qubit only offers a simple superposition of two states and single-qubit gates only make a rotation in the Bloch sphere. The key ingredient to circumvent these limitations is to allow for multiple data re-uploading. A quantum circuit can then be organized as a series of data re-uploading and single-qubit processing units. Furthermore, both data re-uploading and measurements can accommodate multiple dimensions in the input and several categories in the output, to conform to a universal quantum classifier. The extension of this idea to several qubits enhances the efficiency of the strategy as entanglement expands the superpositions carried along with the classification. Extensive benchmarking on different examples of the single- and multi-qubit quantum classifier validates its ability to describe and classify complex data.

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Said, Taoufik, Abdelhaq Chouikh, Zoubida Sakhi, and Mohamed Bennai. "Dynamics of one two-level-atom interacting with a multiple cavity modes." Quantum Information and Computation 23, no. 11&12 (September 2023): 924–36. http://dx.doi.org/10.26421/qic23.11-12-2.

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We discuss how to implement quantum logic gates by considering a two-level-atom driven by a strong microwave field and successively interacting with m+1 cavity modes. The scheme is insensitive to the initial state of the atom, and the operation time is independent of the number of cavity modes involved in the system operations. This scheme is used to realize two quantum logic gates (m-target-qubit controlled-global-phase gate and Multi-qubit phase shift gate) in a time much shorter than the photonic lifetime. We also studied the influence of decoherence on the fidelity. In general, our system is reasonably less sensitive to the photonic and atomic decay rates and therefore it can be experimentally realized.

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Cai, Zhenyu, Michael A. Fogarty, Simon Schaal, Sofia Patomäki, Simon C. Benjamin, and John J. L. Morton. "A Silicon Surface Code Architecture Resilient Against Leakage Errors." Quantum 3 (December 9, 2019): 212. http://dx.doi.org/10.22331/q-2019-12-09-212.

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Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98% fidelity and are improving rapidly. However, there are other types of error --- such as charge leakage and propagation --- that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design.

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Jang, Wonho, Koji Terashi, Masahiko Saito, Christian W. Bauer, Benjamin Nachman, Yutaro Iiyama, Ryunosuke Okubo, and Ryu Sawada. "Initial-State Dependent Optimization of Controlled Gate Operations with Quantum Computer." Quantum 6 (September 8, 2022): 798. http://dx.doi.org/10.22331/q-2022-09-08-798.

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There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivity, and coherence times, a quantum circuit optimization is essential to make the best use of near-term quantum devices. We introduce a new circuit optimizer called AQCEL, which aims to remove redundant controlled operations from controlled gates, depending on initial states of the circuit. Especially, the AQCEL can remove unnecessary qubit controls from multi-controlled gates in polynomial computational resources, even when all the relevant qubits are entangled, by identifying zero-amplitude computational basis states using a quantum computer. As a benchmark, the AQCEL is deployed on a quantum algorithm designed to model final state radiation in high energy physics. For this benchmark, we have demonstrated that the AQCEL-optimized circuit can produce equivalent final states with much smaller number of gates. Moreover, when deploying AQCEL with a noisy intermediate scale quantum computer, it efficiently produces a quantum circuit that approximates the original circuit with high fidelity by truncating low-amplitude computational basis states below certain thresholds. Our technique is useful for a wide variety of quantum algorithms, opening up new possibilities to further simplify quantum circuits to be more effective for real devices.

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Rowell, E. C., Y. Zhang, Y. S. Wu, and M. L. Ge. "Extraspecial two-Groups, generalized Yang-Baxter equations and braiding quantum gates." Quantum Information and Computation 10, no. 7&8 (July 2010): 685–702. http://dx.doi.org/10.26421/qic10.7-8-8.

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In this paper we describe connections among extraspecial 2-groups, unitary representations of the braid group and multi-qubit braiding quantum gates. We first construct new representations of extraspecial 2-groups. Extending the latter by the symmetric group, we construct new unitary braid representations, which are solutions to generalized Yang-Baxter equations and use them to realize new braiding quantum gates. These gates generate the GHZ (Greenberger-Horne-Zeilinger) states, for an arbitrary (particularly an \emph{odd}) number of qubits, from the product basis. We also discuss the Yang-Baxterization of the new braid group representations, which describes unitary evolution of the GHZ states. Our study suggests that through their connection with braiding gates, extraspecial 2-groups and the GHZ states may play an important role in quantum error correction and topological quantum computing.

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35

Hasan, M. Arif, Pierre A. Deymier, Keith Runge, and Joshua Levine. "Exploring multi-qubit analogue operations through acoustic wave dynamics." Journal of the Acoustical Society of America 156, no. 4_Supplement (October 1, 2024): A66. https://doi.org/10.1121/10.0035135.

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Quantum computing harnesses quantum phenomena like superposition and entanglement to surpass classical computers, showing promise across various fields. Current techniques utilize qubits in quantum circuits for parallel information processing, though managing and measuring these systems poses significant challenges. We propose a novel approach to simplify executing complex quantum algorithms without relying on multiple quantum gate operations. Our method introduces logical phi-bits—classical counterparts to qubits, using nonlinear acoustic waves in an externally driven acoustic metastructure. We demonstrate that complex multi-phi-bit unitary operations, akin to those in quantum circuits, can be conducted through a single action on this metastructure. This method starkly contrasts traditional quantum computing, which requires decomposed sequences of qubit gates for equivalent operations. The phi-bit system simplifies processes that are typically complex in quantum mechanics, potentially enhancing robustness and ease of implementation. Our results indicate that phi-bits could expand computational models by merging classical wave dynamics with quantum computational principles, thereby widening the potential of computational technologies. This research advances quantum-analogue computation and introduces new prospects for utilizing wave physics in information processing, thereby challenging and expanding existing paradigms in both classical and quantum computing. [Funding: NSF grant 2204382, 2204400, and 2242925.]

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36

Xiang, Yi, Liang Tang, Ming-Qiang Bai, and Zhi-Wen Mo. "Multi-party quantum secret sharing based on logical GHZ-type states against collective noise." Modern Physics Letters B 35, no. 25 (August 16, 2021): 2150436. http://dx.doi.org/10.1142/s0217984921504364.

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In this paper, we discussed the local preparation methods of two types of multi-qubit logical GHZ-type states using controlled quantum gates, and drew the corresponding quantum circuits. Subsequently, we investigated the measurement-related properties of logical GHZ-type state and thus proposed two multi-party quantum secret sharing schemes against collective-dephasing and collective-rotation noise, respectively. Further, we demonstrated that the schemes can effectively resist some familiar attack strategies. Finally, we analyzed the quantum efficiency of our schemes and made a comprehensive comparison with previous similar schemes.

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Chen, Junjie, Yuxuan Yan, and You Zhou. "Magic of quantum hypergraph states." Quantum 8 (May 21, 2024): 1351. http://dx.doi.org/10.22331/q-2024-05-21-1351.

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Magic, or nonstabilizerness, characterizes the deviation of a quantum state from the set of stabilizer states, playing a fundamental role in quantum state complexity and universal fault-tolerant quantum computing. However, analytical and numerical characterizations of magic are very challenging, especially for multi-qubit systems, even with a moderate qubit number. Here, we systemically and analytically investigate the magic resource of archetypal multipartite quantum states—quantum hypergraph states, which can be generated by multi-qubit controlled-phase gates encoded by hypergraphs. We first derive the magic formula in terms of the stabilizer Rényi-α entropies for general quantum hypergraph states. If the average degree of the corresponding hypergraph is constant, we show that magic cannot reach the maximal value, i.e., the number of qubits n. Then, we investigate the statistical behaviors of random hypergraph states' magic and prove a concentration result, indicating that random hypergraph states typically reach the maximum magic. This also suggests an efficient way to generate maximal magic states with random diagonal circuits. Finally, we study hypergraph states with permutation symmetry, such as 3-complete hypergraph states, where any three vertices are connected by a hyperedge. Counterintuitively, such states can only possess constant or even exponentially small magic for α≥2. Our study advances the understanding of multipartite quantum magic and could lead to applications in quantum computing and quantum many-body physics.

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Dzurak, A. S., M. Y. Simmons, A. R. Hamilton, R. G. Clark, R. Brenner, T. M. Buehler, N. J. Curson, et al. "Construction of a silicon-based solid state quantum computer." Quantum Information and Computation 1, Special (December 2001): 82–95. http://dx.doi.org/10.26421/qic1.s-8.

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We discuss progress towards the fabrication and demonstration of a prototype silicon-based quantum computer. The devices are based on a precise array of 31P dopants embedded in 28Si. Fabrication is being pursued via two complementary pathways – a ‘top-down’ approach for near-term production of few-qubit demonstration devices and a ‘bottom-up’ approach for large-scale qubit arrays. The ‘top-down’ approach employs ion implantation through a multi-layer resist structure which serves to accurately register the donors to metal control gates and single-electron transistor (SET) read-out devices. In contrast the ‘bottom-up’ approach uses STM lithography and epitaxial silicon overgrowth to construct devices at an atomic scale. Techniques for qubit read-out, which utilise coincidence measurements on novel twin-SET devices, are also presented.

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Huang, Chunhui, and Bichun Wu. "High fidelity quantum teleportation assistance with quantum neural network." Modern Physics Letters B 28, no. 24 (September 20, 2014): 1450189. http://dx.doi.org/10.1142/s0217984914501899.

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In this paper, a high fidelity scheme of quantum teleportation based on quantum neural network (QNN) is proposed. The QNN is composed of multi-bit control-not gates. The quantum teleportation of a qubit state via two-qubit entangled channels is investigated by solving the master equation in Lindblad operators with a noisy environment. To ensure the security of quantum teleportation, the indirect training of QNN is employed. Only 10% of teleported information is extracted for the training of QNN parameters. Then the outputs are corrected by the other QNN at Bob's side. We build a random series of numbers ranged in [0, π] as inputs and simulate the properties of our teleportation scheme. The results show that the fidelity of quantum teleportation system is significantly improved to approach 1 by the error-correction of QNN. It illustrates that the distortion can be eliminated perfectly and the high fidelity of quantum teleportation could be implemented.

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Ma, Guangsheng, and Hongbo Li. "Quantum Fully Homomorphic Encryption by Integrating Pauli One-time Pad with Quaternions." Quantum 6 (December 1, 2022): 866. http://dx.doi.org/10.22331/q-2022-12-01-866.

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Quantum fully homomorphic encryption (QFHE) allows to evaluate quantum circuits on encrypted data. We present a novel QFHE scheme, which extends Pauli one-time pad encryption by relying on the quaternion representation of SU(2). With the scheme, evaluating 1-qubit gates is more efficient, and evaluating general quantum circuits is polynomially improved in asymptotic complexity. Technically, a new encrypted multi-bit control technique is proposed, which allows to perform any 1-qubit gate whose parameters are given in the encrypted form. With this technique, we establish a conversion between the new encryption and previous Pauli one-time pad encryption, bridging our QFHE scheme with previous ones. Also, this technique is useful for private quantum circuit evaluation. The security of the scheme relies on the hardness of the underlying quantum capable FHE scheme, and the latter sets its security on the learning with errors problem and the circular security assumption.

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41

Hu, Shi, Wen-Xue Cui, Qi Guo, Hong-Fu Wang, Ai-Dong Zhu, and Shou Zhang. "Multi-qubit non-adiabatic holonomic controlled quantum gates in decoherence-free subspaces." Quantum Information Processing 15, no. 9 (June 15, 2016): 3651–61. http://dx.doi.org/10.1007/s11128-016-1362-4.

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42

Ren, Jun, Jun Yuan, and Xiangdong Zhang. "Multi-qubit quantum phase gates based on surface plasmons of a nanosphere." Journal of the Optical Society of America B 31, no. 2 (January 7, 2014): 229. http://dx.doi.org/10.1364/josab.31.000229.

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43

Niu, Siyuan, and Aida Todri-Sanial. "Enabling Multi-programming Mechanism for Quantum Computing in the NISQ Era." Quantum 7 (February 16, 2023): 925. http://dx.doi.org/10.22331/q-2023-02-16-925.

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NISQ devices have several physical limitations and unavoidable noisy quantum operations, and only small circuits can be executed on a quantum machine to get reliable results. This leads to the quantum hardware under-utilization issue. Here, we address this problem and improve the quantum hardware throughput by proposing a Quantum Multi-programming Compiler (QuMC) to execute multiple quantum circuits on quantum hardware simultaneously. This approach can also reduce the total runtime of circuits. We first introduce a parallelism manager to select an appropriate number of circuits to be executed at the same time. Second, we present two different qubit partitioning algorithms to allocate reliable partitions to multiple circuits – a greedy and a heuristic. Third, we use the Simultaneous Randomized Benchmarking protocol to characterize the crosstalk properties and consider them in the qubit partition process to avoid the crosstalk effect during simultaneous executions. Finally, we enhance the mapping transition algorithm to make circuits executable on hardware using a decreased number of inserted gates. We demonstrate the performance of our QuMC approach by executing circuits of different sizes on IBM quantum hardware simultaneously. We also investigate this method on VQE algorithm to reduce its overhead.

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44

Oddi, Angelo, and Riccardo Rasconi. "Analyzing Heuristic-based Randomized Search Strategies for the Quantum Circuit Compilation Problem." Fundamenta Informaticae 174, no. 3-4 (September 28, 2020): 259–81. http://dx.doi.org/10.3233/fi-2020-1942.

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In this work we investigate the performance of greedy randomised search (GRS) techniques to the problem of compiling quantum circuits to emerging quantum hardware. Quantum computing (QC) represents the next big step towards power consumption minimisation and CPU speed boost in the future of computing machines. Quantum computing uses quantum gates that manipulate multi-valued bits (qubits). A quantum circuit is composed of a number of qubits and a series of quantum gates that operate on those qubits, and whose execution realises a specific quantum algorithm. Current quantum computing technologies limit the qubit interaction distance allowing the execution of gates between adjacent qubits only. This has opened the way to the exploration of possible techniques aimed at guaranteeing nearest-neighbor (NN) compliance in any quantum circuit through the addition of a number of so-called swap gates between adjacent qubits. In addition, technological limitations (decoherence effect) impose that the overall duration (makespan) of the quantum circuit realization be minimized. One core contribution of the paper is the definition of two lexicographic ranking functions for quantum gate selection, using two keys: one key acts as a global closure metric to minimise the solution makespan; the second one is a local metric, which favours the mutual approach of the closest qstates pairs. We present a GRS procedure that synthesises NN-compliant quantum circuits realizations, starting from a set of benchmark instances of different size belonging to the Quantum Approximate Optimization Algorithm (QAOA) class tailored for the MaxCut problem. We propose a comparison between the presented meta-heuristics and the approaches used in the recent literature against the same benchmarks, both from the CPU efficiency and from the solution quality standpoint. In particular, we compare our approach against a reference benchmark initially proposed and subsequently expanded in [1] by considering: (i) variable qubit state initialisation and (ii) crosstalk constraints that further restrict parallel gate execution.

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Zwerver, A. M. J., T. Krähenmann, T. F. Watson, L. Lampert, H. C. George, R. Pillarisetty, S. A. Bojarski, et al. "Qubits made by advanced semiconductor manufacturing." Nature Electronics 5, no. 3 (March 2022): 184–90. http://dx.doi.org/10.1038/s41928-022-00727-9.

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AbstractFull-scale quantum computers require the integration of millions of qubits, and the potential of using industrial semiconductor manufacturing to meet this need has driven the development of quantum computing in silicon quantum dots. However, fabrication has so far relied on electron-beam lithography and, with a few exceptions, conventional lift-off processes that suffer from low yield and poor uniformity. Here we report quantum dots that are hosted at a 28Si/28SiO2 interface and fabricated in a 300 mm semiconductor manufacturing facility using all-optical lithography and fully industrial processing. With this approach, we achieve nanoscale gate patterns with excellent yield. In the multi-electron regime, the quantum dots allow good tunnel barrier control—a crucial feature for fault-tolerant two-qubit gates. Single-spin qubit operation using magnetic resonance in the few-electron regime reveals relaxation times of over 1 s at 1 T and coherence times of over 3 ms.

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Chia, Nai-Hui, Ching-Yi Lai, and Han-Hsuan Lin. "Efficient learning of t-doped stabilizer states with single-copy measurements." Quantum 8 (February 12, 2024): 1250. http://dx.doi.org/10.22331/q-2024-02-12-1250.

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One of the primary objectives in the field of quantum state learning is to develop algorithms that are time-efficient for learning states generated from quantum circuits. Earlier investigations have demonstrated time-efficient algorithms for states generated from Clifford circuits with at most log⁡(n) non-Clifford gates. However, these algorithms necessitate multi-copy measurements, posing implementation challenges in the near term due to the requisite quantum memory. On the contrary, using solely single-qubit measurements in the computational basis is insufficient in learning even the output distribution of a Clifford circuit with one additional T gate under reasonable post-quantum cryptographic assumptions. In this work, we introduce an efficient quantum algorithm that employs only nonadaptive single-copy measurement to learn states produced by Clifford circuits with a maximum of O(log⁡n) non-Clifford gates, filling a gap between the previous positive and negative results.

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Secchi, Andrea, and Filippo Troiani. "Multi-Dimensional Quantum Capacitance of the Two-Site Hubbard Model: The Role of Tunable Interdot Tunneling." Entropy 25, no. 1 (December 31, 2022): 82. http://dx.doi.org/10.3390/e25010082.

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Few-electron states confined in quantum-dot arrays are key objects in quantum computing. The discrimination between these states is essential for the readout of a (multi-)qubit state, and can be achieved through a measurement of the quantum capacitance within the gate-reflectometry approach. For a system controlled by several gates, the dependence of the measured capacitance on the direction of the oscillations in the voltage space is captured by the quantum capacitance matrix. Herein, we apply this tool to study a double quantum dot coupled to three gates, which enable the tuning of both the bias and the tunneling between the two dots. Analytical solutions for the two-electron case are derived within a Hubbard model, showing the overall dependence of the quantum capacitance matrix on the applied gate voltages. In particular, we investigate the role of the tunneling gate and reveal the possibility of exploiting interdot coherences in addition to charge displacements between the dots. Our results can be directly applied to double-dot experimental setups, and pave the way for further applications to larger arrays of quantum dots.

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48

Jang, Wonho, Koji Terashi, Masahiko Saito, Christian W. Bauer, Benjamin Nachman, Yutaro Iiyama, Tomoe Kishimoto, Ryunosuke Okubo, Ryu Sawada, and Junichi Tanaka. "Quantum Gate Pattern Recognition and Circuit Optimization for Scientific Applications." EPJ Web of Conferences 251 (2021): 03023. http://dx.doi.org/10.1051/epjconf/202125103023.

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There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivities, and coherence times, circuit optimization is essential to make the best use of quantum devices produced over a next decade. We introduce two separate ideas for circuit optimization and combine them in a multi-tiered quantum circuit optimization protocol called AQCEL. The first ingredient is a technique to recognize repeated patterns of quantum gates, opening up the possibility of future hardware optimization. The second ingredient is an approach to reduce circuit complexity by identifying zero- or low-amplitude computational basis states and redundant gates. As a demonstration, AQCEL is deployed on an iterative and effcient quantum algorithm designed to model final state radiation in high energy physics. For this algorithm, our optimization scheme brings a significant reduction in the gate count without losing any accuracy compared to the original circuit. Additionally, we have investigated whether this can be demonstrated on a quantum computer using polynomial resources. Our technique is generic and can be useful for a wide variety of quantum algorithms.

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Oliveira, Michael de, Luís S. Barbosa, and Ernesto F. Galvão. "Quantum advantage in temporally flat measurement-based quantum computation." Quantum 8 (April 9, 2024): 1312. http://dx.doi.org/10.22331/q-2024-04-09-1312.

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Several classes of quantum circuits have been shown to provide a quantum computational advantage under certain assumptions. The study of ever more restricted classes of quantum circuits capable of quantum advantage is motivated by possible simplifications in experimental demonstrations. In this paper we study the efficiency of measurement-based quantum computation with a completely flat temporal ordering of measurements. We propose new constructions for the deterministic computation of arbitrary Boolean functions, drawing on correlations present in multi-qubit Greenberger, Horne, and Zeilinger (GHZ) states. We characterize the necessary measurement complexity using the Clifford hierarchy, and also generally decrease the number of qubits needed with respect to previous constructions. In particular, we identify a family of Boolean functions for which deterministic evaluation using non-adaptive MBQC is possible, featuring quantum advantage in width and number of gates with respect to classical circuits.

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Tholén, Mats O., Riccardo Borgani, Giuseppe Ruggero Di Carlo, Andreas Bengtsson, Christian Križan, Marina Kudra, Giovanna Tancredi, et al. "Measurement and control of a superconducting quantum processor with a fully integrated radio-frequency system on a chip." Review of Scientific Instruments 93, no. 10 (October 1, 2022): 104711. http://dx.doi.org/10.1063/5.0101398.

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We describe a digital microwave platform called Presto, designed for measurement and control of multiple quantum bits (qubits) and based on the third-generation radio-frequency system on a chip. Presto uses direct digital synthesis to create signals up to 9 GHz on 16 synchronous output ports, while synchronously analyzing responses on 16 input ports. Presto has 16 DC-bias outputs, four inputs and four outputs for digital triggers or markers, and two continuous-wave outputs for synthesizing frequencies up to 15 GHz. Scaling to a large number of qubits is enabled through deterministic synchronization of multiple Presto units. A Python application programming interface configures a firmware for synthesis and analysis of pulses, coordinated by an event sequencer. The analysis integrates template matching (matched filtering) and low-latency (184–254 ns) feedback to enable a wide range of multi-qubit experiments. We demonstrate Presto’s capabilities with experiments on a sample consisting of two superconducting qubits connected via a flux-tunable coupler. We show single-shot readout and active reset of a single qubit; randomized benchmarking of single-qubit gates showing 99.972% fidelity, limited by the coherence time of the qubit; and calibration of a two-qubit iSWAP gate.

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Journal articles on the topic 'Multi-qubit quantum gates'

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