Robust Entanglement Gates for Trapped-Ion Qubits

Shapira, Yotam; Shaniv, Ravid; Manovitz, Tom; Akerman, Nitzan; Ozeri, Roee

doi:10.1103/physrevlett.121.180502

Cited by 95 publications

(85 citation statements)

References 23 publications

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“…In general the Bell state fidelity F is a function of F , G and A [23]. For the sin 2 pulse, we find that all derivatives of the fidelity ∂ n F (F,G,A) ∂t n | t=τ k in the motional ground state, n = 0, are equal to 0, demonstrating the intrinsic resilience against timing imperfections.…”

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confidence: 82%

Robust and Resource-Efficient Microwave Near-Field Entangling Be+9 Gate

et al. 2019

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Microwave trapped-ion quantum logic gates avoid spontaneous emission as a fundamental source of decoherence. However, microwave two-qubit gates are still slower than laser-induced gates and hence more sensitive to fluctuations and noise of the motional mode frequency. We propose and implement amplitude-shaped gate drives to obtain resilience to such frequency changes without increasing the pulse energy per gate operation. We demonstrate the resilience by noise injection during a two-qubit entangling gate with 9 Be + ion qubits. In absence of injected noise, amplitude modulation gives an operation infidelity in the 10 −3 range.Trapped ions are a leading platform for scalable quantum logic [1, 2] and quantum simulations [3]. Major challenges towards larger-scale devices include the integration of tasks and components that have been so far only demonstrated individually, as well as single and multiqubit gates with the highest possible fidelity to reduce the overhead in quantum error correction. Microwave control of trapped-ion qubits has the potential to address both challenges [4,5] as it allows the gate mechanism, potentially including control electronics, to be integrated into scalable trap arrays. Because spontaneous emission as a fundamental source of decoherence is absent and microwave fields are potentially easier to control than the laser beams that are usually employed, microwaves are a promising approach for high fidelity quantum operations. In fact, microwave two-qubit gate fidelities seem to improve more rapidly than laser-based gates. However, observed two-qubit gate speeds of laser-based gates [6,7] are still about an order of magnitude faster than for microwave gates [8][9][10]. This makes gates more susceptible to uncontrolled motional mode frequency changes, as transient entanglement with the motional degrees of freedom is the key ingredient in multi-qubit gates for trapped ions. As other error sources have been addressed recently, this is of growing importance. Merely increasing Rabi frequencies may not be the most resource-efficient approach, as it will increase energy dissipation in the device. A more efficient use of available resources could be obtained using pulse shaping or modulation techniques. In fact, a number of recent advances in achieving highfidelity operations or long qubit memory times have been proposed or obtained by tailored control fields. Examples include pulsed dynamic decoupling [11], Walsh modulation [12], additional dressing fields to increase coherence times [13], phase [14], amplitude [15][16][17][18][19][20] and fre-quency modulation [21] as well multi-tone fields [22][23][24]. In many cases, these techniques lead to significant advantages. For multi-qubit gates, one mechanism is to optimize the trajectory of the motional mode in phase space for minimal residual spin-motional entanglement in case of experimental imperfections. This effectively reduces the distance between the origin and the point in phase space at which the gate terminates in case of errors.Here we propo...

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confidence: 82%

Robust and Resource-Efficient Microwave Near-Field Entangling Be+9 Gate

et al. 2019

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“…Thus we fix 2M degrees of freedom of the driving field such that ω n = 2π T n and φ n = π 2 for n = 1, ..., M . Choosing a harmonic basis for the gate drive has already been proven useful in several entangling gate schemes [13,19,25].…”

Section: All-to-all Entanglement Gate Derivationmentioning

confidence: 99%

“…We are motivated by Ω 2 |r| 2 1 being the peak laser power during the gate. Furthermore, we are conceptually searching for generalized solutions of physically-motivated schemes which are in general spectrally sparse [13,18,19,40]. We intend to violate this sparsity only weakly.…”

Section: All-to-all Entanglement Gate Derivationmentioning

confidence: 99%

“…Below we describe the matrix elements of L which correspond to the different properties. The elements L j,n are given, which correspond to conditions applicable to the j'th normal mode and the n'th tone with frequency ω n = 2π T n. The desired property is obtained by satisfying the relation N n=1 L j,n r n = 0 for all j. Robustness to timing errors, i.e error of the form T → T + δT , can be implemented by requiring that dGj dδT | δT =0,ω= 2π T n = 0, and dFj dδT | δT =0,ω= 2π T n = 0 [19]. We note that substitution of the harmonic frequencies should be done after differentiation (since the choice of frequencies does not depend on this kind of error).…”

Section: Appendix III Explicit Expression For Robustness Propertiesmentioning

confidence: 99%

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Theory of robust multiqubit nonadiabatic gates for trapped ions

et al. 2020

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The prevalent approach to executing quantum algorithms on quantum computers is to break-down the algorithms to a concatenation of universal gates, typically single and two-qubit gates. However such a decomposition results in long gate sequences which are exponential in the qubit register size. Furthermore, gate fidelities tend to decrease when acting in larger qubit registers. Thus high-fidelity implementations in large qubit registers is still a prominent challenge. Here we propose and investigate multi-qubit entangling gates for trapped-ions. Our gates couple many qubits at once, allowing to decrease the total number of gates used while retaining a high gate fidelity. Our method employs all of the normal-modes of motion of the ion chain, which allows to operate outside of the adiabatic regime and at rates comparable to the secular ion-trapping frequency. Furthermore we extend our method for generating Hamiltonians which are suitable for quantum analog simulations, such as a nearest-neighbour spin Hamiltonian or the Su-Schrieffer-Heeger Hamiltonian.

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“…Currently, the most performing multi‐qubit operations rely on a controlled‐phase type of gate that was originally proposed from Mølmer and Sørensen, whose formal expression is given in Equation . The details of the specific implementation of these gates depend on the qubit type . In general, they require only global control lasers to entangle multiple qubits, hence avoiding beams to be independently focused on each ion (which may anyway be necessary, for example, for single‐qubit control).…”

Section: Experimental Achievements and Prospective Technologiesmentioning

confidence: 99%

Quantum Computers as Universal Quantum Simulators: State‐of‐the‐Art and Perspectives

et al. 2019

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The past few years have witnessed the concrete and fast spreading of quantum technologies for practical computation and simulation. In particular, quantum computing platforms based on either trapped ions or superconducting qubits have become available for simulations and benchmarking, with up to few tens of qubits that can be reliably initialized, controlled, and measured. The present Review aims at giving a comprehensive outlook on the state‐of‐the‐art capabilities offered from these near‐term noisy devices as universal quantum simulators, that is, programmable quantum computers potentially able to calculate the time evolution of many physical models. First, a pedagogic overview on the basic theoretical background pertaining digital quantum simulations is given, with a focus on hardware‐dependent mapping of spin‐type Hamiltonians into the corresponding quantum circuit as a key initial step toward simulating more complex models. Then, the main experimental achievements obtained in the last decade are reviewed, focusing on the digital quantum simulation of such spin models by employing two leading quantum architectures. Their performances are compared, and future challenges are outlined, also in view of prospective hybrid technologies, towards the ultimate goal of reaching the long‐sought quantum advantage for the simulation of complex many‐body models in the physical sciences.

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Robust Entanglement Gates for Trapped-Ion Qubits

Cited by 95 publications

References 23 publications

Robust and Resource-Efficient Microwave Near-Field Entangling Be+9 Gate

Robust and Resource-Efficient Microwave Near-Field Entangling Be+9 Gate

Theory of robust multiqubit nonadiabatic gates for trapped ions

Quantum Computers as Universal Quantum Simulators: State‐of‐the‐Art and Perspectives

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