Coherence of a dynamically decoupled single neutral atom

Abstract

Long qubit coherence and efficient atom–photon coupling are essential for advanced applications in quantum communication. One technique to maintain coherence is dynamical decoupling (DD), where a periodic sequence of refocusing pulses is employed to reduce the interaction of the system with the environment. We experimentally study the implementation of DD on an optically trapped, spin-polarized 87 R b atom. We use the two magnetic-sensitive 5 S 1 / 2 Zeeman levels | F = 2 , m F = − 2 ⟩ and | F = 1 , m F = − 1 ⟩ as qubit states, motivated by the possibility of coupling | F = 2 , m F = − 2 ⟩ to 5 P 3 / 2 the excited state | F ′ = 3 , m F ′ = − 3 ⟩ via a closed optical transition. With more refocusing pulses in the DD technique, we manage to extend the coherence time from 38(3) µs to around 7 ms. We also observe a strong correlation between the motional states of the atom and the qubit coherence after the refocusing, which can be used as a measurement basis to resolve trapping parameters.

Measuring the environment of a Cs qubit with dynamical decoupling sequences

“…We want to underline that we have assumed a heuristic decay with exp −(T/τ c ) 2 in equation (2). To validate this assumption, we can now compare this decay to the analytical result in equation (20) which predicts a decay with exp −(T/τ c ) 1+α ≈ exp −(T/τ c ) 1.89 . Consequently, the accurate result obtained from equation ( 2) can be explained by the exponent α = 0.89 (2) which is close to one.…”

“…For the calculation of χ N , we calculate the coherence integral in equation ( 15) with the expected form of the spectral density in equation ( 6) and the filter function given by equation ( 17) for every number N of π-pulses. This assures that we also take into account small-N effects which are not present in the analytical result shown in equation (20). Importantly, each N-CPMG data set owns its specific amplitude V 0 and offset b.…”

“…Equation (20) shows that the exponent α can directly be inferred from the visibility V(T) [27,28,44]. The latter exhibits an exponential behavior where the exponent of the argument is 1 + α, determined by the algebraic behavior of the spectral density.…”

“…The primary purpose of dynamical decoupling is the effective reduction of the coupling between the qubit and a mostly generic environment by a sequence of pulses. These single [4] and multi-pulse sequences [5][6][7][8] have already been used to extend coherence in various physical systems, ranging from spin ensembles [9], semiconductor quantum dots [10,11], nitrogen-vacancy centers in diamond [12,13], superconducting qubits [14], ensembles of ultracold atoms and ions [15][16][17] to the limit of single atoms and ions [18][19][20]. Consequently, many key characteristics and possible causes of qubit decoherence in ultracold atomic systems have already been discussed and explained in various experimental and theoretical works [21][22][23][24][25][26].…”

“…Remarkably, such sequences cannot only be utilised to partially reverse the decoherence dynamics but also to perform noise spectroscopy, i.e. to measure details of the coupled, unknown degrees of freedom of the environment [14,20,[27][28][29][30][31]. This first appears to be counter-intuitive since sensing is usually more effective if the coupling between the probe and the measurement object is strong.…”