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Item type:Publication, Access status: with files , General, efficient, and robust Hamiltonian engineeringImplementing the time evolution under a desired target Hamiltonian is critical for various applications in quantum science. Due to the exponential increase of parameters in the system size and due to experimental imperfections, this task can be challenging in quantum many-body settings. We introduce an efficient and robust scheme to engineer arbitrary local many-body Hamiltonians. To this end, our scheme applies single-qubit π or π/2 pulses to an always-on system Hamiltonian, which we assume to be native to a given platform. These sequences are constructed by efficiently solving a linear program (LP) which minimizes the total evolution time. In this way, we can engineer target Hamiltonians that are only limited by the locality of the interactions in the system Hamiltonian. Based on average Hamiltonian theory and by using robust composite pulses, we make our schemes robust against errors, including finite-pulse-time errors and various control errors. To demonstrate the performance of our scheme, we provide numerical simulations. In particular, we solve the Hamiltonian-engineering problem on a laptop for arbitrary two-local Hamiltonians on a two-dimensional square lattice with 196 qubits in only 60 s. Moreover, we simulate the engineering of general Heisenberg Hamiltonians from Ising Hamiltonians with imperfect single-qubit pulses for smaller system sizes, and achieve a fidelity larger than 99.9%, which is orders of magnitude better than nonrobust implementations.Publicationtype: Journal Article29 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Bosonic Randomized Benchmarking with Passive Transformations(American Physical Society (APS), 2025-04-07); ; ; Randomized benchmarking (RB) is the most commonly employed protocol for the characterization of unitary operations in quantum circuits due to its reasonable experimental requirements and robustness against state preparation and measurement (SPAM) errors. So far, the protocol has been limited to discrete or fermionic systems, whereas extensions to bosonic systems have been unclear for a long time due to challenges arising from the underlying bosonic Hilbert space. In this work, we close the gap for bosonic systems and develop an RB protocol to benchmark passive Gaussian transformations on any particle-number subspace, hich we call passive bosonic RB. The protocol is built on top of the recently developed filtered RB framework [J. Helsen et al., PRX Quantum 3, 020357 (2022), M. Heinrich et al., Randomized benchmarking with random quantum circuits, arxiv:2212.06181 [quant-ph]] and is designed to isolate the multitude of exponential decays arising for passive bosonic transformations. We give explicit formulas and a Julia implementation for the necessary postprocessing of the experimental data. We also analyze the sampling complexity of passive bosonic RB by deriving analytical expressions for the variance. They show a mild scaling with the number of modes, suggesting that passive bosonic RB is experimentally feasible for a moderate number of modes. We focus on experimental settings involving Fock states and particle-number-resolving measurements, but also discuss Gaussian settings, deriving the first results for heterodyne measurements.Publicationtype: Journal Article20 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Efficient Hamiltonian engineering(2024-10-25); ; We propose a novel and efficient scheme to engineer arbitrary (local) many-body Hamiltonians by interleaving the free evolution of a fixed system Hamiltonian with layers of single-qubit Pauli or Clifford gates. These sequences are constructed by solving a linear program (LP) which minimizes the total evolution time. The target Hamiltonians that can be engineered by our method are only limited by the locality of the Pauli terms in the system Hamiltonian. We then construct an efficient relaxation of this LP with a classical runtime that depends on the number of Pauli terms in the Pauli decomposition of the system Hamiltonian and is thus a low-degree polynomial in the number of qubits in practice. With our method, it is also possible to engineer Hamiltonians if only partial knowledge of the system Hamiltonian is available, which can be used to cancel unknown unwanted Pauli terms. We show the classical efficiency of our method by engineering an arbitrary two-body Hamiltonian on a 2D square lattice with $225$ qubits in only $60$ seconds. We also provide numerical simulations of our method modelling an ion trap device with an Ising Hamiltonian and engineering a general Heisenberg Hamiltonian. Moreover, we address dominant error sources in practical applications.Publicationtype: Preprint63 63 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Time-optimal multi-qubit gates : complexity, efficient heuristic and gate-time bounds(2024-03-13); ; 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.Publicationtype: Journal Article47 63 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Time-optimal multi-qubit gates : complexity, efficient heuristic and gate-time bounds(2023-07-20); ; Multi-qubit interactions are omnipresent in quantum computing hardware, and they can generate multi-qubit entangling gates. Such gates promise advantages over traditional two-qubit gates. In this work, we focus on the quantum gate synthesis with multi-qubit Ising-type interactions and single-qubit gates. These interactions can generate global ZZ-gates (GZZ gates). We show that the synthesis of time-optimal multi-qubit gates is NP-hard. However, under certain assumptions we provide explicit constructions of time-optimal multi-qubit gates allowing for efficient synthesis. These constructed multi-qubit gates have a constant gate time and can be implemented with linear single-qubit gate layers. Moreover, a heuristic algorithm with polynomial runtime for synthesizing fast multi-qubit gates is provided. Finally, we prove lower and upper bounds on the optimal GZZ gate-time. Furthermore, we conjecture that any GZZ gate can be executed in a time O(n) for n qubits. We support this claim with theoretical and numerical results.Publicationtype: Preprint47 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Synthesis of and compilation with time-optimal multi-qubit gates(Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften, 2023-04-20); ; ; ; Huber, PatrickWe 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 n 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.Publicationtype: Journal Article76 30