Ion-Based Quantum Sensor for Optical Cavity Photon Numbers

Abstract

We dispersively couple a single trapped ion to an optical cavity to extract information about the cavity photon-number distribution in a nondestructive way. The photon-number-dependent AC-Stark shift experienced by the ion is measured via Ramsey spectroscopy. We use these measurements first to obtain the ion-cavity interaction strength. Next, we reconstruct the cavity photon-number distribution for coherent states and for a state with mixed thermal-coherent statistics, finding overlaps above 99% with the calibrated states.Cavity quantum electrodynamics (cavity QED) provides a conceptually simple and powerful platform for probing the quantized interaction between light and matter [1]. Early experiments opened a window into the dynamics of coherent atom-photon interactions, first through observations of collective Rabi oscillations and vacuum Rabi splittings [2][3][4][5] and later at the single-atom level [6][7][8][9][10][11]. More recently, building on measurements of the cavity field via the atomic phase [12,13], cavity photon statistics have been analyzed in experiments with Rydberg atoms or superconducting qubits in microwave resonators [14][15][16][17], culminating in the generation and stabilization of nonclassical cavity field states [18][19][20][21][22][23][24]. These experiments operate in a dispersive regime, in which information about the cavity field can be extracted via the qubits with minimal disturbance to the field [1].In parallel, it was pointed out that the Jaynes-Cummings Hamiltonian that describes cavity QED also describes the interaction of light and ions in a harmonic trapping potential [25]. This interaction underpins the generation of nonclassical states of motion [26][27][28][29] and the implementation of gates between trapped ions [30]. In analogy to the phase shifts experienced by qubits due to the cavity field, ions experience quantized AC-Stark shifts due to their coupling to the harmonic trap potential [31]. These shifts have been characterized using techniques similar to those introduced in Ref. [12]. Here, we have transferred the principle of dispersive measurement to an ion qubit coupled to a cavity. In contrast to experiments with flying Rydberg atoms, the ion is strongly confined; in contrast to both Rydberg and superconducting-qubit experiments, our cavity operates in the optical regime.We employ a single trapped 40 Ca + ion as a quantum sensor [32] to extract information about cavity photons without destroying them. Via Ramsey spectroscopy of the ion, we measure the phase shift and dephasing of the ion's state, both of which result from the interaction of the ion with the cavity field. The phase shift is induced by the mean number of cavity photons due to the AC-Stark effect, and the dephasing is caused by uncertainties in the cavity photon number. Reconstructing the cavity photon-number distribution from these measurements allows us to determine the mean and the width of the distribution and thus to distinguish between states with coherent photon statistics and mixed thermal-co...

Strong Photon Blockade Mediated by Optical Stark Shift in a Single-Atom–Cavity System

“…Furthermore, the scheme for realizing quantum interference and strong vacuum Rabi splitting beyond the strong-coupling limit could also be applied to explore high-quality multiphoton blockade, e.g., photon-pair sources could be obtained by apply-ing destructive quantum interference to a three-photon excitation [77]. With slight modifications, our proposal can be extended to various systems, including a singlequantum-dot-cavity model [78,79] and a singe-ion-cavity model [80][81][82], which provide several interesting opportunities for exploring the fundamentals of quantum optics, and potential applications in single-photon transistors, all-optical switching, and quantum metrology [39,83,84].…”

Numerical investigation of a segmented-blade ion trap with biasing rods

“…Second, from the perspective of quantum networks and distributed quantum computing, optical interface with the segmented-blade trap was mostly done with high-NA lenses so far [18,33,34]. Alternatively, we point out that it would also be interesting to combine the trap with optical cavities [35][36][37]. It would be informative if future theoretical studies could include a strategy for coupling fiber cavities [38][39][40], the influence of dielectric surface charges to the trap potential [41], and the impact of high voltage on piezoelectric transducer (for scanning the cavity length) to the potential energy.…”

Locking Multi-Laser Frequencies to a Precision Wavelength Meter: Application to Cold Atoms

“…In quantum metrology, it is necessary to minimize the frequency instability for developing a precise and accurate atomic clock [ 3 ]. In many instances of quantum optics and quantum information, it is indispensable to stabilize the laser frequency within a range narrower than a target atomic or cavity linewidth, in order to trap and cool atoms [ 4 , 5 , 6 ] and ions [ 7 ], or to probe cavity modes of a high- Q resonator [ 8 , 9 ]. To this end, a standard approach is to employ the well-known Pound–Drever–Hall (PDH) method [ 10 ].…”