Quantum process tomography of a Mølmer-Sørensen gate via a global beam

Abstract

We present a framework for quantum process tomography of two-ion interactions that leverages modulations of the trapping potential and composite pulses from a global laser beam to achieve individual-ion addressing. Tomographic analysis of identity and delay processes reveals dominant error contributions from laser decoherence and slow qubit frequency drift during the tomography experiment. We use this framework on two co-trapped 40 Ca + ions to analyze both an optimized and an overpowered Mølmer-Sørensen gate and to compare the results of this analysis to a less informative Bell-state tomography measurement and to predictions based on a simplified noise model. These results show that the technique is effective for the characterization of two-ion quantum processes and for the extraction of meaningful information about the errors present in the system. The experimental convenience of this method will allow for more widespread use of process tomography for characterizing entangling gates in trapped-ion systems.

Quantum process tomography of the single-shot entangling gate with superconducting qubits

“…Such an approach has been experimentally validated using superconducting devices, measured with quantum state tomography [1][2][3][4]. However, these approaches would complicate the quantum circuits if only single-and two-qubit operations are available, especially for a large number of qubits, and thus the characterization of most algorithms is still hard compared to a single-shot as well as with ion trap systems to characterize two-and three-qubit quantum gates [17][18][19]. In this paper, following our theoretical proposal in [10], we numerically investigate the time evolution of an entangling gate requiring only a single step for creating a GHZ-maximally-entangled state, under realistic parameters of a transmon-cavity system.…”

Process Tomography on a 7-Qubit Quantum Processor via Tensor Network Contraction Path Finding

“…As such, estimating the O(2 4n )-sized Choi matrix [5,6] which uniquely describes the process on n qubits through the standard QPT procedure scales exponentially in time. This prohibitive time cost has limited the use of the standard QPT procedure to general processes on up to 2 or 3 qubits [7][8][9][10][11][12][13].…”

Transport-enabled entangling gate for trapped ions

“…Transport operations are essential to most modern ion trap experiments to enable loading, individual detection, and individual addressing [1,2]. Maturing trap design and electrical potential control hardware have led to impressive feats of fast shuttling [3,4], fast ion separation [5,6], optical phase control [7], junction transport [4,8], and ion chain rotation [9,10].…”

“…A radio-frequency potential with 176 V amplitude at 56.4 MHz applied to long electrodes on both sides of the trap axis provides radial confinement. Arbitrary waveform generators (AWGs) deliver potentials with a max-imum amplitude of ±12 V and a 5 ns sampling rate to 42 segmented electrodes to control the strength and location of the axial potential minimum [7]. The centerof-mass (COM) and breathing-motion (BM) axial mode frequencies are ω COM /(2π) = 1.41 MHz and ω BM /(2π) = 2.45 MHz [16].…”