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arXiv:1905.05385 · Physical Review A

Control of spontaneous emission of qubits from weak to strong coupling

Wai‐Keong Mok, Jia-Bin You, Wenzu Zhang, Wan-Li Yang, Ching Eng Png

Published May 28, 2019• 4 citations
arXivHTMLPDF

Abstract

Photon emission and absorption by an individual qubit are essential elements for the quantum manipulation of light. Here we demonstrate the controllability of spontaneous emission of a qubit in various electromagnetic environments. The parameter regimes that allow for flexible control of the qubit emission routes are comprehensively discussed. By properly tuning the system couplings and decay rates, the spontaneous emission rate of the qubit can undergo Purcell enhancement and inhibition. In particular, when the cavity is prepared in the excited state, the spontaneous emission rate of the qubit can be significantly suppressed. We also demonstrate a spectral filter effect which can be realized by controlling the steady-state emission spectra of qubits.

DOI
10.1103/physreva.99.053847

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Photon emission and absorption by an individual qubit are essential elements for the quantum manipulation of light. Here we demonstrate the controllability of spontaneous emission of a qubit in various electromagnetic environments. The parameter regimes that allow for flexible control of the qubit emission routes are comprehensively discussed. By properly tuning the system couplings and decay rates, the spontaneous emission rate of the qubit can undergo Purcell enhancement and inhibition. In particular, when the cavity is prepared in the excited state, the spontaneous emission rate of the qubit can be significantly suppressed. We also demonstrate a spectral filter effect which can be realized by controlling the steady-state emission spectra of qubits.
Spontaneous emission into micro- or nano-scale structures can be enhanced or inhibited by engineering the local density of optical states using closed quantum cavities. When electromagnetic fields are confined within small mode volumes of a high-Q symmetrical closed quantum cavity, the Purcell effect significantly accelerates the natural spontaneous emission. Due to the statistical nature of spontaneous emission, the emitted fields do not have a well-defined phase; consequently, the emission is incoherent and lacks directional control. The situation becomes more complicated in multi-mode cavities, as selecting a specific mode in a particular direction requires precise detuning between the emitter transition frequency and the cavity mode frequency to ensure strong coupling. In single-mode cavities, only the dominant mode can resonate, and only in a specific direction; thus, an appropriate transition frequency range can be easily determined. Such cavities allow for greater manipulation of the local electromagnetic density of states, facilitating effective control of the direction of spontaneous emission. This property is essential for creating efficient single-photon sources, photonic circuits, and on-chip quantum information.
Abstract The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons’ waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.
The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons' waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.
Spontaneous emission through a coupled cavity can be a significant decay channel for qubits in circuit quantum electrodynamics. We present a circuit design that effectively eliminates spontaneous emission due to the Purcell effect while maintaining strong coupling to a low-Q cavity. Excellent agreement over a wide range in frequency is found between measured qubit relaxation times and the predictions of a circuit model. Using fast (nanosecond time-scale) flux biasing of the qubit, we demonstrate in situ control of qubit lifetime over a factor of 50. We realize qubit reset with 99.9% fidelity in 120 ns.
Abstract Inhibition and enhancement of spontaneous emission rate, first proposed by Purcell, is discussed in terms of altered density-of-modes in various types of solid-state cavities and the Purcell factor is derived for two-level atomic system. The conditions for observing Purcell factor and experimental findings in micropillars embedded with Quantum Dots (QD)s are discussed. The strong interaction between photons and matter in the form of QD excitons, dispersion relations for ground and excited states separated by Rabi splitting are discussed. Experimental photoluminescence spectra showing anticrossing of exciton lines and cavity lines by temperature and other tuning methods are used to illustrate the strong light-matter interaction. The Jayness–Cummins model based on second quantization is presented to point out Rabi oscillation, Purcell effect, and other novel features. Microcavity structures for observing cavity quantum electrodynamics effects are mentioned. Microcavity lasers predicting thresholdless operation for unity spontaneous emission coupling factors are discussed.
Impressive progress has been achieved in controlling the spontaneous emission rate for emitters in Nanophotonic structures, such as microcavities, photonic crystals and nano-antennas. In all cases, however, the modification of the emission is stationary in time. Thus, the emission rate is time-independent and the distribution of photon emission times are stochastic and follow an exponential distribution in the weak coupling regime. In this paper, by using fast all-optical switching of a microcavity, the cavity resonance is tuned within tens of picosesonds. This drastically changes the local optical density of states at the emission frequency within the emission lifetime of the emitters. This paper theoretically studied an ensemble of two-level sources with a time dependent decay rate and have derived the excited state population and emitted intensity as a function of time for continuous wave and pulsed excitation. Deterministic bursts of dramatically enhanced or inhibited emission intensity within short intervals. Thereby, we control the photon distribution to show behavior that strongly deviates from single exponential decay. This can be used to protect quantum information systems against decoherence and to realize non-Markovian dynamics in cavity quantum electrodynamics.