Robust Population Transfer Research Articles

Coherent manipulation of noise-protected superconducting artificial atoms in the Lambda scheme

We propose a new protocol for thr manipulation of a three-level artificial atom in Lambda ($\Lambda$) configuration in the absence of a direct pump coupling. It allows faithful, selective and robust population transfer analogous to stimulated Raman adiabatic passage ($\Lambda$-STIRAP), in highly noise protected superconducting artificial atoms. It combines the use of a two-photon pump pulse with suitable advanced control, operated by a slow modulation of the phase of the external fields, leveraging on the stability of semiclassical microwave drives. This protocol is a building block for novel tasks in complex quantum architectures. Its demonstration would be a benchmark for the implementation of a class of multilevel advanced control procedures for quantum computation and microwave quantum photonics in systems based on artificial atoms.

Coherent superpositions of states in coupled Hilbert-space using step by step Morris–Shore transformation

Creation of coherent superpositions in quantum systems with Na states in the lower set and Nb states in the upper set is presented. The solution is drived by using the Morris–Shore transformation, which step by step reduces the fully coupled system to a three-state Λ-like system and a set of decoupled states. It is shown that, for properly timed pulse, robust population transfer from an initial ground state (or superposition of M ground states) to an arbitrary coherent superposition of the ground states can be achieved by coincident pulses and/or STIRAP techniques.

Adiabatic passage mediated by plasmons: A route towards a decoherence-free quantum plasmonic platform

We show that the interaction of surface plasmons with quantum emitters can be described by an effective model that has the same structure as a lossy multimode cavity quantum electromagnetic interaction. This allows the coherent manipulation of quantum emitters dressed by surface plasmons at the nanoscale. We show that strong coupling in quantum plasmonics can be used to mediate efficiently the interaction between emitters via a decoherence-free channel, immune to the strong plasmon dissipation. Efficient and robust population transfer, as well as the deterministic generation of entanglement between emitters are numerically shown. These results pave the way for an efficient use of the quantum plasmonic platform beyond its inherent losses.

Efficient frequency conversion based on local optimization theory

We discuss theoretically a robustness of the difference frequency conversion method and demonstrate it by numerical simulation. This technique, borrowed from an analogous scheme of robust population transfer in atomic physics and nuclear magnetic resonance called ‘local optimization’, can keep the intermediate frequency fixed and make the counterintuitive ordering emerge automatically. Here we show an efficient frequency conversion in two-process three wave mixing (TWM). And because the local optimization method is a well-defined, automated computational procedure, we think it would be very useful in the efficient conversion of complicated multi-process TWM, which is a difficult subject in STIRAP.

Population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states

We investigate the selective and efficient population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states by time-separated chirped pump and Stokes pulses. We show that it is possible to achieve selective, efficient, and robust population transfer from either of the equally populated initial doublet states to either of the final ground doublet levels by merging stimulated Raman adiabatic passage and chirped adiabatic passage techniques. Moreover, the maximal coherent superpositions between either of the initial doublet states and either of the final doublet states, between the intermediate level and either of the final doublet states, or between the final doublet levels can be achieved by varying the chirp rates and single-photon detuning of the pump and Stokes pulses. This method may have potential applications in quantum coherent control of population dynamics in realistic atomic or molecular systems with equally populated initial and empty final manifolds.

Coherent injecting, extracting, and velocity filtering of neutral atoms in a ring trap via spatial adiabatic passage

We introduce a coherent technique to inject, extract, and velocity filter neutral atoms in a ring trap coupled via tunneling to two additional waveguides. By adiabatically following the transverse spatial dark state, the proposed technique allows for an efficient and robust velocity dependent atomic population transfer between the ring and the input/output waveguides. We have derived explicit conditions for the spatial adiabatic passage that depend on the atomic velocity along the input waveguide as well as on the initial population distribution among the transverse vibrational states. The validity of our proposal has been checked by numerical integration of the corresponding two-dimensional Schrödinger equation with state-of-the-art parameter values for 87Rb atoms and an optical dipole ring trap.

High-fidelity population transfer in a Josephson three-level atom with optimized level anharmonicity

We propose a theoretical scheme to enhance the fidelity of population transfer in a Josephson three-level atom by optimizing the level anharmonicity. Without the leakage effect, the ideal population transfer can be performed via Raman adiabatic passage. In the general case, we consider the dependence of transfer fidelity on the leakage error, and then present an effective way to implement the high-fidelity population transfer using the optimized level structure. The scheme could offer a potential route towards the robust population transfer with artificial Josephson atoms experimentally.

Breakdown of adiabatic transfer of light in waveguides in the presence of absorption

In atomic physics, adiabatic evolution is often used to achieve a robust and efficient population transfer. Many adiabatic schemes have also been implemented in optical waveguide structures. Recently there has been increasing interest in the influence of decay and absorption, and their engineering applications. Here it is shown that even a small decay can significantly influence the dynamical behavior of a system, above and beyond a mere change of the overall norm. In particular, a small decay can lead to a breakdown of adiabatic transfer schemes, even when both the spectrum and the eigenfunctions are only sightly modified. This is demonstrated for the generalization of a stimulated Raman adiabatic passage scheme that has recently been implemented in optical waveguide structures. Here the question how an additional absorption in either the initial or the target waveguide influences the transfer property of the scheme is addressed. It is found that the scheme breaks down for small values of the absorption at a relatively sharp threshold, which can be estimated by simple analytical arguments.

Fast and robust population transfer in two-level quantum systems with dephasing noise and/or systematic frequency errors

We design, by invariant-based inverse engineering, driving fields that invert the population of a two-level atom in a given time, robustly with respect to dephasing noise and/or systematic frequency shifts. Without imposing constraints, optimal protocols are insensitive to the perturbations but need an infinite energy. For a constrained value of the Rabi frequency, a flat $\ensuremath{\pi}$ pulse is the least sensitive protocol to phase noise but not to systematic frequency shifts, for which we describe and optimize a family of protocols.

Population transfer and generation of arbitrary superpositions of quantum states in a four-level system using a single-chirped laser pulse

We propose a scheme for coherent control of population transfer and arbitrary superpositions of quantum states by a single-chirped laser pulse in a Λ-type excited-doublet four-level system. It is shown that selective, efficient, and robust population transfer from the initial state to the target states (excited or ground) can be achieved via chirped adiabatic passage when the pulse bandwidth is smaller than about 1/10 of the energy separations between the excited-doublet levels and between the ground states. Moreover, arbitrary coherent superpositions between the excited-doublet states, or between the higher ground state and either of the excited-doublet states, can be created by appropriately tuning the chirp rate and detuning the laser field. The proposed flexible method of coherent control of population transfer and arbitrary superpositions between the initially unpopulated states requires only a single pulse, and is robust against variations in the laser parameters, which has potential applications in quantum information processing.

Chirped laser excitation of quantum dot excitons coupled to a phonon bath

Motivated by recent experimental results, we present a detailed account of adiabatic population transfer in InGaAs/GaAs quantum dots by strong chirped laser pulses. Specifically, numerical simulations in very good agreement with experimental results allow for a clear physical picture of this process. An analytical expression is developed, which is used to analyze the strong-field adiabatic population transfer in the presence of the phonon environment. Optimal pulse parameters to achieve robust population transfer at temperatures as high as 80 K are identified and are confirmed by numerical simulations.

Selective and efficient control of population transfer in the presence of an equally populated initial doublet

We present a way to realize selective, robust, and efficient population transfer in a ladder-type four-level system with an equally populated doublet in the initial state. By merging stimulated Raman adiabatic passage and chirped adiabatic passage techniques, we show that selective and complete population transfer from either of the initial doublet levels to the final state can be achieved with chirped pump and Stokes pulse pairs when the spectral resolution constraint of a frequency swept pulse holds (the energy separation of doublet levels should be much larger than the pulse bandwidth). We further demonstrate that the spectral resolution of selective population transfer can be enhanced significantly by using pump pulse pair and Stokes pulse due to temporal quantum interference between the sequential transitions in the time domain, which can also be well followed as a result of the frequency-domain formation of a comblike structure of the pulse pair spectrum. The proposals take into account the case of population transfer in realistic atomic and molecular systems, and may have applications in quantum coherent control of systems with equally populated initial manifolds.

Dynamic transition from complete population transfer to self-induced transparency

We explore the connection between adiabatic rapid passage, a technique that allows for robust complete population transfer (CPT) in a resonant absorber, and self-induced transparency solitons. We employ the auxiliary differential equation finite-difference time-domain method to fully resolve the dynamics of femtosecond light pulses propagating through an absorbing two-level medium. Using the example of linearly chirped Gaussian pulses we find that the pulses achieving robust CPT for a single two-level system are also pulses that will transform into solitary waves when incident on a resonantly absorbing medium. At the entrance into the absorber strongly chirped, adiabatic pulses completely transfer the electronic population from the ground to the upper state. As the pulses suffer absorption they undergo a dynamic transition and quickly split into an off-resonant radiation part and one or several unchirped solitary pulses that may carry away some of the initially achieved population inversion. This spectral and temporal transformation process limits the spatial depths of the region of CPT in a dense absorber regardless of the initial pulse amplitude. We also show that the frequency-domain pulse area, defined as the spectral amplitude at the resonance frequency, allows for a better distinction between the regimes of $2\ensuremath{\pi}$-pulse and $0\ensuremath{\pi}$-pulse formation than time-domain measurements.

Superposition of states by adiabatic passage inN-pod systems

We study the stimulated Raman adiabatic passage technique in an $N$-pod system driven by $N$ pulsed fields when $N\ensuremath{-}2$ and $N\ensuremath{-}1$ pulses not connected to the initial state have the same shape. We show that, for properly timed pulses, robust population transfer from an initial ground state to an arbitrary coherent superposition of the ground states can be achieved in a single step. The case of $N\ensuremath{-}2$ pulses of the same shape involves a geometric phase of the same type as the one appearing in tripod systems.

Ultrafast coherent population transfer driven by two few-cycle laser pulses

We investigate ultrafast coherent population transfer driven by few-cycle pump and Stokes laser pulses in the Λ-type three-level system with the stimulated Raman adiabatic passage technique beyond the rotating-wave approximation. In contrast to the case with the rotating wave approximation, the most efficient population transfer may be realized without the satisfaction of the one-photon resonances or two-photon resonance and the transfer efficiency depends critically on the Rabi frequencies and initial optical phases of the two laser fields when the peak Rabi frequencies are much larger than the respective transition frequencies. Moreover, complete and robust population transfer can still be obtained with the variations of the Rabi frequencies, pulse durations, and one-photon or two-photon detuning in a moderate range, though a considerable transient population may reside in the excited state. These abnormal behaviors result from the counterrotating terms, which are not taken into account in the traditional rotating wave approximation.

Ultrafast stimulated Raman parallel adiabatic passage by shaped pulses

We present a general and versatile technique of population transfer based on {\it parallel adiabatic passage} by femtosecond shaped pulses. Their amplitude and phase are specifically designed to optimize the adiabatic passage corresponding to parallel eigenvalues at all times. We show that this technique allows the robust adiabatic population transfer in a Raman system with the total pulse area as low as 3 $\pi$, corresponding to a fluence of one order of magnitude below the conventional stimulated Raman adiabatic passage process. This process of short duration, typically pico- and subpicosecond, is easily implementable with the modern pulse shaper technology and opens the possibility of ultrafast robust population transfer with interesting applications in quantum information processing.

Robust adiabatic sum frequency conversion

We discuss theoretically and demonstrate experimentally the robustness of the adiabatic sum frequency conversion method. This technique, borrowed from an analogous scheme of robust population transfer in atomic physics and nuclear magnetic resonance, enables the achievement of nearly full frequency conversion in a sum frequency generation process for a bandwidth up to two orders of magnitude wider than in conventional conversion schemes. We show that this scheme is robust to variations in the parameters of both the nonlinear crystal and of the incoming light. These include the crystal temperature, the frequency of the incoming field, the pump intensity, the crystal length and the angle of incidence. Also, we show that this extremely broad bandwidth can be tuned to higher or lower central wavelengths by changing either the pump frequency or the crystal temperature. The detailed study of the properties of this converter is done using the Landau-Zener theory dealing with the adiabatic transitions in two level systems.

Piecewise Adiabatic Population Transfer in a Molecule via a Wave Packet

We propose a class of schemes for robust population transfer between quantum states that utilize trains of coherent pulses, thus forming a generalized adiabatic passage via a wave packet. We study piecewise stimulated Raman adiabatic passage with pulse-to-pulse amplitude variation, and piecewise chirped Raman passage with pulse-to-pulse phase variation, implemented with an optical frequency comb. In the context of production of ultracold ground-state molecules, we show that with almost no knowledge of the excited potential, robust high-efficiency transfer is possible.

Population Transfer between Two Quantum States by Piecewise Chirping of Femtosecond Pulses: Theory and Experiment

We propose and experimentally demonstrate the method of population transfer by piecewise adiabatic passage between two quantum states. Coherent excitation of a two-level system with a train of ultrashort laser pulses is shown to reproduce the effect of an adiabatic passage, conventionally achieved with a single frequency-chirped pulse. By properly adjusting the amplitudes and phases of the pulses in the excitation pulse train, we achieve complete and robust population transfer to the target state. The piecewise nature of the process suggests a possibility for the selective population transfer in complex quantum systems.

Dipole mediated tunnelling: Robust single-pulse population transfer across dipolar double-well systems

Single pulse dipole mediated tunnelling at frequencies tuned approximately to the vicinity of the direct 1-photon and multiphoton tunnel transitions is explored as a mechanism of population transfer across asymmetric dipolar 3-level lambda- (Λ-) or N-level extended Λ-systems. These systems may be purely sequentially coupled, with zero dipole matrix coupling elements for non-neighbouring states along the legs of the Λ. In simulations for model systems with typical molecular parameters, dipole mediated tunnelling is found to be a highly efficient strong-field mechanism of population transfer with remarkable robustness properties, in particular so for higher-order multiphoton processes.