Coherent population trapping with a controlled dissipation: applications in optical metrology

Abstract

We analyze the properties of a pulsed coherent population trapping protocol that uses a controlled decay from the excited state in a Λ-level scheme. We study this problem analytically and numerically and find regimes where narrow transmission, absorption, or fluorescence spectral lines occur. We then look for optimal frequency measurements using these spectral features by computing the Allan deviation in the presence of ground state decoherence and show that the protocol is on a par with Ramsey-CPT. We discuss possible implementations with ensembles of alkali atoms and single ions and demonstrate that typical pulsed-CPT experiments that are realized on femto-second timescales can be implemented on micro-seconds timescales using this scheme.Since its observation [1], coherent-population-trapping (CPT) and its counterpart electromagneticallyinduced-transparency (EIT) [2] have enabled a wide range of experimental achievements. Using a three-level Λ-scheme and exploiting a quantum interference effect in the excited state, coherent transfer of population (STIRAP) between vibrational states [3], efficient cooling of atoms [4], precise atomic clocks [5,6], or light storage [7,8] have been realized. Ramsey-CPT schemes have also been shown to improve the sensitivity of frequency measurements by removing power broadening issues [6]. Further, pulsed-CPT schemes have been investigated theoretically [9][10][11][12][13][14] and experimentally using femto-second lasers [15][16][17] with implications for multimode quantum memories [18].Recently, a novel pulsed-CPT scheme was realized by engineering a Λ-system in the microwave domain and exploiting the hyperfine interaction between the electron spin of a nitrogen-vacancy (NV) defect in diamond and a nearby 13 C nuclear spin [19]. The originality of the experiment is that relaxation was externally controlled through optical pumping by a far detuned laser that couples the excited state to the ground state in the Λ-system via a metastable state. By externally controlled dissipation, we mean that the decay from the excited state to the two ground states in the Λ scheme can be triggered at will. In general such a scheme with controlled relaxation is useful for atomic systems where the excited state population lifetime is too long compared to the decoherence mechanisms. Further, compared to schemes where spontaneous emission takes place during the excitation, this method can be used to measure the excited state population while the dark state is being prepared.In this work, we analyze such a pulsed-CPT scheme with a controlled decay from the excited state, both analytically and numerically. We show that interleaving sequences of unitary and fully dissipative steps gives rise to narrow dark transmission and photoluminescence spectral lines whose widths do not depend upon the spontaneous emission rate but solely upon the control pulse area and number of steps. Then, we discuss implications of this scheme for metrology and estimate its precision compared to Ramsey-CPT. Finally, we present...

Optimization of a quantum control sequence for initializing an NV spin register

“…We write the states in the notation |m s , m I in this paper. A coherent population trapping (CPT) protocol couples an initial and a target state to an intermediate excited state by applying coherent electromagnetic fields, which trap the population in the superposition of the initial and the target states [29,30]. However, in our case, instead of applying coherent driving fields simultaneously, we sequentially apply MW, RF and optical pulses to drive the population between the initial state |0, ±1 and the target state |0, 0 through certain intermediate states.…”

Effect of inter-system crossing rates and optical illumination on the polarization of nuclear spins nearby nitrogen-vacancy centers

“…This approach can be also understood by means of coherent population trapping (see Ref. [33] for details).…”

Coherent Microwave Control of a Nuclear Spin Ensemble at Room Temperature

“…In atomic CPT, the transitions are in the optical domain, so the dissipative preparation of the dark state occurs through spontaneous emission. Interestingly, in the case of NV centers, dissipation is tunable via the green laser that polarizes the NV spin [16,48]. One consequence of this is nuclear spin dephasing and relaxation induced by the optical excitation [49][50][51][52].…”