Magnetically Induced Optical Transparency on a Forbidden Transition in Strontium for Cavity-Enhanced Spectroscopy

Abstract

In this work we realize a narrow spectroscopic feature using a technique that we refer to as magnetically-induced optical transparency. A cold ensemble of 88 Sr atoms interacts with a single mode of a high-finesse optical cavity via the 7.5 kHz linewidth, spin forbidden 1 S0 to 3 P1 transition. By applying a magnetic field that shifts two excited state Zeeman levels, we open a transmission window through the cavity where the collective vacuum Rabi splitting due to a single level would create destructive interference for probe transmission. The spectroscopic feature approaches the atomic transition linewidth, which is much narrower than the cavity linewidth, and is highly immune to the reference cavity length fluctuations that limit current state-of-the-art laser frequency stability.There has been a dedicated effort in recent years to improve the frequency stability of lasers [1] used to probe optical atomic clocks [2][3][4]. Improvements in these precision measurement technologies are essential for advancing a broad range of scientific pursuits such as searching for variations in fundamental constants [5] , gravitational wave detection [6,7], and physics beyond the standard model [8,9]. Associated improvements in atomic clocks would also advance recent work on relativistic geodesy [10].The frequency stability of current state-of-the-art lasers is limited by thermal fluctuations in the reference cavity mirror coatings, substrates, and spacer [11]. This problem can be alleviated by creating systems that rely on an ensemble of atoms, rather than the reference cavity, to achieve stable optical coherence. Recent approaches include cavity-assisted non-linear spectroscopy [12][13][14] and superradiant lasers [15][16][17][18]. Both approaches use narrow forbidden transitions with linewidths ranging from 7.5 kHz to 1 mHz. These novel systems are absolute frequency references and are intrinsically less sensitive to both fundamental thermal and technical vibrations that create noise on the optical cavity's resonance frequency.Here we demonstrate a new linear spectroscopy approach in which a static magnetic field can induce optical transparency in the transmission spectrum of an optical cavity. The center frequency of the transparency window is shown to be insensitive to changes in the cavityresonance frequency and to first-order Zeeman shifts. The observed linewidth of the feature approaches the natural linewidth of the 7.5 kHz optical transition and can be insensitive to inhomogeneous broadening of the atomic transition frequency. The linewidth of the feature is an important attribute for laser stabilization, as a laser stabilized to a narrow spectroscopic feature is less sensitive to technical offsets than a laser stabilized to a broader feature. In the future, it might be possible to extend this technique to even narrower optical transitions for enhanced spectroscopic sensitivity in atoms such as calcium and magnesium.In partial analogy to electromagnetically induced transparency (EIT) [19][20][21], we refer to this eff...

Tunable Photon blockade with single atom in a cavity under electromagnetically induced transparency

“…In fact, the analogous proposal by utilizing dipole-forbidden transition has been realized experimentally in cavity enhanced magnetically induced optical transparency on 88 Sr atomic ensembles in Ref. [63]. Moreover, we should note that the elaborately selective long-lived state in our model can also be employed by utilizing the clock transition, owing to the unique energy-level structures for alkaline-earth-metal atoms [64][65][66].…”

“…In our numerical simulation, we take the cavity decay rate = 2 × 160 kHz, which has been realized in recent experiment of superradiance for 87 Sr clock transition [62], the atomic spontaneous decay rate = 2 × 7.5 kHz for the long-lived excited state of 3 1 , the weak cavity driven strength / = 0.1, and the single atom-cavity coupling / = 4, for which coupling strength on a forbidden transition has demonstrated capability in current experiments for single atoms trapped in the cavity with the quantization length of the cavity around a few millimeters [15,63]. Therefore, the free parameters in our system are reduced to cavity-light detuning Δ , Rabi frequency of the control field Ω, and optical Stark shift 0 by continuously tuning the sign and strength of Zeeman splitting ℏΔ in experiment [63]. Limited by the validity of our model, the numerical results presented below exhibit the parameter space 0 ≤ 0 / ≤ 4, corresponding the tunable magnetic field around a few tens of Gauss.…”

Squeezed lasing

“…Our results can be understood from the perspective of the physics of drivendissipative systems, where the extraordinary spectral purity of a laser emerges as the result of a second-order driven dissipative transition above which the Liouvillian gap is closed and coherence times diverge [3][4][5]. The squeezed laser opens the possibility to extend the range of applicability of narrowband non-classical states of light for bandwith-limited atom optics [6][7][8][9] and metrology [10][11][12], by capitalizing on the progress in the development of ultra-narrowband atom optics and lasers [3,13,14]. The quest for light-sources with narrow frequency spectra is motivated by applications such as quantum computing with trapped ions [15,16], optical atomic clocks [17,18], ground-state cooling of nanomechanical systems [19,20], gravitational-wave detection [21,22] geosciences [23] and tests of fundamental physics [24].…”

“…(a) Zero-delay secondorder correlation function versus Cs for three values of squeezing parameter r and nq = 50. Dashed lines correspond to the limit in the lasing regime given by Eq (14)…”

Intracavity Rydberg-atom electromagnetically induced transparency using a high-finesse optical cavity

“…A number of review articles exist on various specific topics, e.g., Rydberg atom interactions [4,5], quantum information with Rydberg atoms [6,7], Rydberg atoms in magnetic fields [8] and microwave field sensing with Rydberg atoms [9]. New experiments and theory, where collective Rydberg excitations created in ultracold gases are used to shape electro-magnetic fields at the quantum level, are beginning to attract increasing attention [10][11][12][13][14][15][16][17][18][19][20][21][22].…”