Stroboscopic approach to trapped-ion quantum information processing with squeezed phonons

Abstract

In trapped-ion quantum information processing, interactions between spins (qubits) are mediated by collective modes of motion of an ion crystal. While there are many different experimental strategies to design such interactions, they all face both technical and fundamental limitations to the achievable coherent interaction strength. In general, obtaining strong interactions and fast gates is an ongoing challenge. Here, we extend previous work [Phys. Rev. Lett. 112, 030501 (2019)] and present a general strategy for enhancing the interaction strengths in trapped-ion systems via parametric amplification of the ions' motion. Specifically, we propose a stroboscopic protocol using alternating applications of parametric amplification and spin-motion coupling. In comparison with the previous work, we show that the current protocol can lead to larger enhancements in the coherent interaction that increase exponentially with the gate time.

Schrödinger cat states of a macroscopic charged particle co-trapped with an ion

“…with Ω P A an interaction strength and φ P A the phase of the modulation. The use of such terms has been considered in the context of quantum computing with trapped ions to speed up entangling gates [24,25]; these references also provide a thorough analysis of the limiting factors of the approach and discuss various operation sequences which optimize the outcome fidelity.…”

“…Using the commutation relation (25) to interchange position with the displacement operator gives rise to an additional infinitesimal displacement given by:…”

Quantum amplification of boson-mediated interactions

“…Bosonmediated interactions can in principle be amplified through parametric driving of the boson channel; the drive need not couple directly to the interacting quantum objects. This technique has been proposed for a variety of quantum platforms [14][15][16][17][18][19][20][21][22][23][24] , but has not to date been realized in the laboratory. Here we experimentally demonstrate the amplification of a boson-mediated interaction between two trapped-ion qubits by parametric modulation of the trapping potential 21 .…”

“…Achieving high fidelity generally requires that the effective interaction strength must dominate the characteristic rates of decoherence in the system. Recent theoretical proposals [14][15][16][17][18][19][20][21][22][23][24] offer a way to increase the bosonmediated interaction strength through parametric modulation. When decoherence of the quantum objects to be coupled-including decoherence due to control fields used to implement the coupling 34 -is the primary source of infidelity, this technique can reduce that infidelity by decreasing the required interaction duration.…”

“…Here θ is the relative phase between the parametric drive and the coupling interaction in the first term. This general Hamiltonian can be realized in many physical systems including trapped ions 21,22 , cavity optomechanics 15 , and superconducting circuit quantum electrodynamics (QED) or atom-cavity systems 17,18 . For interactions between trapped-ion qubits, the â and â † operators typically correspond to a normal mode of ion motion in the trap (whose excitations are phonons) and ŝi = σi j , where σi j is a Pauli operator for the i th ion with j ∈ {x, y, z} 11,12,35,36 .…”