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  Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 374 journals)
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Quantum Science and Technology
Number of Followers: 15  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Online) 2058-9565
Published by IOP Homepage  [45 journals]
  • Reducing hardware requirements for entanglement distribution via joint
           hardware-protocol optimization

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      Authors: Adrià Labay Mora; Francisco Ferreira da Silva Stephanie Wehner
      First page: 045001
      Abstract: We conduct a numerical investigation of fiber-based entanglement distribution over distances of up to 1600 km using a chain of processing-node quantum repeaters. We determine minimal hardware requirements while simultaneously optimizing over protocols for entanglement generation and entanglement purification, as well as over strategies for entanglement swapping. Notably, we discover that through an adequate choice of protocols the hardware improvement cost scales linearly with the distance covered. Our results highlight the crucial role of good protocol choices in significantly reducing hardware requirements, such as employing purification to meet high-fidelity targets and adopting a swap as soon as possible policy for faster rates. To carry out this analysis, we employ an extensive simulation framework implemented with NetSquid, a discrete-event-based quantum-network simulator, and a genetic-algorithm-based optimization methodology to determine minimal hardware requirements.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-01T23:00:00Z
      DOI: 10.1088/2058-9565/ad57e9
      Issue No: Vol. 9, No. 4 (2024)
       
  • Efficient and practical quantum compiler towards multi-qubit systems with
           deep reinforcement learning ∗

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      Authors: Qiuhao Chen; Yuxuan Du, Yuliang Jiao, Xiliang Lu, Xingyao Wu Qi Zhao
      First page: 045002
      Abstract: Efficient quantum compiling is essential for complex quantum algorithms realization. The Solovay–Kitaev (S–K) theorem offers a theoretical lower bound on the required operations for approaching any unitary operator. However, it is still an open question that this lower bound can be actually reached in practice. Here, we present an efficient quantum compiler which, for the first time, approaches the S–K lower bound in practical implementations, both for single-qubit and two-qubit scenarios, marking a significant milestone. Our compiler leverages deep reinforcement learning (RL) techniques to address current limitations in terms of optimality and inference time. Furthermore, we show that our compiler is versatile by demonstrating comparable performance between inverse-free basis sets, which is always the case in real quantum devices, and inverse-closed sets. Our findings also emphasize the often-neglected constant term in scaling laws, bridging the gap between theory and practice in quantum compiling. These results highlight the potential of RL-based quantum compilers, offering efficiency and practicality while contributing novel insights to quantum compiling theory.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-02T23:00:00Z
      DOI: 10.1088/2058-9565/ad420a
      Issue No: Vol. 9, No. 4 (2024)
       
  • Multi-qubit dynamical decoupling for enhanced crosstalk suppression

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      Authors: Siyuan Niu; Aida Todri-Sanial Nicholas T Bronn
      First page: 045003
      Abstract: Dynamical decoupling (DD) is one of the simplest error suppression methods, aiming to enhance the coherence of qubits in open quantum systems. Moreover, DD has demonstrated effectiveness in reducing coherent crosstalk, one major error source in near-term quantum hardware, which manifests from two types of interactions. Static crosstalk exists in various hardware platforms, including superconductor and semiconductor qubits, by virtue of always-on qubit-qubit coupling. Additionally, driven crosstalk may occur as an unwanted drive term due to leakage from driven gates on other qubits. Here we explore a novel staggered DD protocol tailored for multi-qubit systems that suppresses the decoherence error and both types of coherent crosstalk. We develop two experimental setups—an ‘idle–idle’ experiment in which two pairs of qubits undergo free evolution simultaneously and a ‘driven-idle’ experiment in which one pair is continuously driven during the free evolution of the other pair. These experiments are performed on an IBM Quantum superconducting processor and demonstrate the significant impact of the staggered DD protocol in suppressing both types of coherent crosstalk. When compared to the standard DD sequences from state-of-the-art methodologies with the application of X2 sequences, our staggered DD protocol enhances circuit fidelity by 19.7% and 8.5%, respectively, in addressing these two crosstalk types.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-03T23:00:00Z
      DOI: 10.1088/2058-9565/ad5a37
      Issue No: Vol. 9, No. 4 (2024)
       
  • Bases for optimising stabiliser decompositions of quantum states

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      Authors: Nadish de Silva; Ming Yin Sergii Strelchuk
      First page: 045004
      Abstract: Stabiliser states play a central role in the theory of quantum computation. For example, they are used to encode computational basis states in the most common quantum error correction schemes. Arbitrary quantum states admit many stabiliser decompositions: ways of being expressed as a superposition of stabiliser states. Understanding the structure of stabiliser decompositions has significant applications in verifying and simulating near-term quantum computers. We introduce and study the vector space of linear dependencies of n-qubit stabiliser states. These spaces have canonical bases containing vectors whose size grows exponentially in n. We construct elegant bases of linear dependencies of constant size three. Critically, our sparse bases can be computed without first compiling a dictionary of all n-qubit stabiliser states. We utilise them to explicitly compute the stabiliser extent of states of more qubits than is feasible with existing techniques. Finally, we delineate future applications to improving theoretical bounds on the stabiliser rank of magic states.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-07T23:00:00Z
      DOI: 10.1088/2058-9565/ad53fc
      Issue No: Vol. 9, No. 4 (2024)
       
  • Quantum computer-enabled receivers for optical communication

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      Authors: John Crossman; Spencer Dimitroff, Lukasz Cincio Mohan Sarovar
      First page: 045005
      Abstract: Optical communication is the standard for high-bandwidth information transfer in today’s digital age. The increasing demand for bandwidth has led to the maturation of coherent transceivers that use phase- and amplitude-modulated optical signals to encode more bits of information per transmitted pulse. Such encoding schemes achieve higher information density, but also require more complicated receivers to discriminate the signaling states. In fact, achieving the ultimate limit of optical communication capacity, especially in the low light regime, requires coherent joint detection of multiple pulses. Despite their superiority, such joint detection receivers are not in widespread use because of the difficulty of constructing them in the optical domain. In this work we describe how optomechanical transduction of phase information from coherent optical pulses to superconducting qubit states followed by the execution of trained short-depth variational quantum circuits can perform joint detection of communication codewords with error probabilities that surpass all classical, individual pulse detection receivers. Importantly, we utilize a model of optomechanical transduction that captures non-idealities such as thermal noise and loss in order to understand the transduction performance necessary to achieve a quantum advantage with such a scheme. We also execute the trained variational circuits on an IBM-Q device with the modeled transduced states as input to demonstrate that a quantum advantage is possible even with current levels of quantum computing hardware noise.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-07T23:00:00Z
      DOI: 10.1088/2058-9565/ad5abb
      Issue No: Vol. 9, No. 4 (2024)
       
  • Collective biphoton temporal waveform of photon-pair generated from
           Doppler-broadened atomic ensemble

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      Authors: Heewoo Kim; Hansol Jeong Han Seb Moon
      First page: 045006
      Abstract: Photonic quantum states generated from atomic ensembles will play important roles in future quantum networks and long-distance quantum communication because their advantages, such as universal identity and narrow spectral bandwidth, are essential for quantum nodes and quantum repeaters based on atomic ensembles. In this study, we report the collectively coherent superposition of biphoton wavefunction emitted from different velocity classes in a Doppler-broadened cascade-type atomic ensemble. We experimentally demonstrate that the three times difference of temporal width of both biphoton temporal waveforms varies dependent on the wavelengths of the signal and idler photons from both 6S1/2–6P3/2–6D5/2 and –8S1/2 transitions of 133Cs, corresponding to the idler and signal wavelengths of 852 nm–917 nm and 852 nm–795 nm, respectively. Our results help understand the characteristics of biphoton sources from a warm atomic ensemble and can be applied to long-distance quantum networks and practical quantum repeaters based on atom–photon interactions.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-07T23:00:00Z
      DOI: 10.1088/2058-9565/ad5a38
      Issue No: Vol. 9, No. 4 (2024)
       
  • Non-unitary Trotter circuits for imaginary time evolution

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      Authors: Chiara Leadbeater; Nathan Fitzpatrick, David Muñoz Ramo Alex J W Thom
      First page: 045007
      Abstract: We propose an imaginary time equivalent of the well-established Pauli gadget primitive for Trotter-decomposed real time evolution, using mid-circuit measurements on a single ancilla qubit. Imaginary time evolution (ITE) is widely used for obtaining the ground state (GS) of a system on classical hardware, computing thermal averages, and as a component of quantum algorithms that perform non-unitary evolution. Near-term implementations on quantum hardware rely on heuristics, compromising their accuracy. As a result, there is growing interest in the development of more natively quantum algorithms. Since it is not possible to implement a non-unitary gate deterministically, we resort to the implementation of probabilistic ITE (PITE) algorithms, which rely on a unitary quantum circuit to simulate a block encoding of the ITE operator—that is, they rely on successful ancillary measurements to evolve the system non-unitarily. Compared with previous PITE proposals, the suggested block encoding in this paper results in shorter circuits and is simpler to implement, requiring only a slight modification of the Pauli gadget primitive. This scheme was tested on the transverse Ising model and the fermionic Hubbard model and is demonstrated to converge to the GS of the system.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-08T23:00:00Z
      DOI: 10.1088/2058-9565/ad53fb
      Issue No: Vol. 9, No. 4 (2024)
       
  • Interplay among entanglement, measurement incompatibility, and nonlocality

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      Authors: Yuwei Zhu; Xingjian Zhang Xiongfeng Ma
      First page: 045008
      Abstract: Nonlocality, manifested by the violation of Bell inequalities, indicates entanglement within a joint quantum system. A natural question is how much entanglement is required for a given nonlocal behavior. Here, we explore this question by quantifying entanglement using a family of generalized Clauser–Horne–Shimony–Holt-type Bell inequalities. Given a Bell-inequality violation, we derive analytical lower bounds on the entanglement of formation, a measure related to entanglement dilution. The bounds also lead to an analytical estimation of the negativity of entanglement. In addition, we consider one-way distillable entanglement tied to entanglement distillation and derive tight numerical estimates. With the additional assumptions of qubit-qubit systems, we find that the relationship between entanglement and measurement incompatibility is not simply a trade-off under a fixed nonlocal behavior. Furthermore, we apply our results to two realistic scenarios—non-maximally entangled and Werner states. We show that one can utilize the nonlocal statistics by optimizing the Bell inequality for better entanglement estimation.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-09T23:00:00Z
      DOI: 10.1088/2058-9565/ad5aba
      Issue No: Vol. 9, No. 4 (2024)
       
  • Quanto: optimizing quantum circuits with automatic generation of circuit
           identities

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      Authors: Jessica Pointing; Oded Padon, Zhihao Jia, Henry Ma, Auguste Hirth, Jens Palsberg Alex Aiken
      First page: 045009
      Abstract: Existing quantum compilers focus on mapping a logical quantum circuit to a quantum device and its native quantum gates. Only simple circuit identities are used to optimize the quantum circuit during the compilation process. This approach misses more complex circuit identities, which could be used to optimize the quantum circuit further. We propose Quanto, the first quantum optimizer that automatically generates circuit identities. Quanto takes as input a gate set and generates provably correct circuit identities for the gate set. Quanto’s automatic generation of circuit identities includes single-qubit and two-qubit gates, which leads to a new database of circuit identities, some of which are novel to the best of our knowledge. In addition to the generation of new circuit identities, Quanto’s optimizer applies such circuit identities to quantum circuits and finds optimized quantum circuits that have not been discovered by other quantum compilers, including IBM Qiskit and Cambridge Quantum Computing Tket. Quanto’s database of circuit identities could be applied to improve existing quantum compilers and Quanto can be used to generate identity databases for new gate sets.
      Citation: Quantum Science and Technology
      PubDate: 2024-07-11T23:00:00Z
      DOI: 10.1088/2058-9565/ad5b16
      Issue No: Vol. 9, No. 4 (2024)
       
  • Constructive plaquette compilation for the parity architecture

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      Authors: Roeland ter Hoeven; Benjamin E Niehoff, Sagar Sudhir Kale Wolfgang Lechner
      First page: 035056
      Abstract: Parity compilation is the challenge of laying out the required constraints for the parity mapping in a local way. We present the first constructive compilation algorithm for the parity architecture using plaquettes for arbitrary higher-order optimization problems. This enables adiabatic protocols, where the plaquette layout can natively be implemented, as well as fully parallelized digital circuits. The algorithm builds a rectangular layout of plaquettes, where in each layer of the rectangle at least one constraint is added. The core idea is that each constraint, consisting of any qubits on the boundary of the rectangle and some new qubits, can be decomposed into plaquettes with a deterministic procedure using ancillas. We show how to pick a valid set of constraints and how this decomposition works. We further give ways to optimize the ancilla count and show how to implement optimization problems with additional constraints.
      Citation: Quantum Science and Technology
      PubDate: 2024-06-30T23:00:00Z
      DOI: 10.1088/2058-9565/ad5a36
      Issue No: Vol. 9, No. 3 (2024)
       
 
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  Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 374 journals)
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