Destructive Quantum Interference Research Articles

Coupled field induced conversion between destructive and constructive quantum interference

We study the control of quantum interference in a four-level atom driven by three coherent fields forming a closed loop. The spontaneous emission spectrum shows two sets of peaks which are dramatically influenced by the fields. Due to destructive quantum interference, a dark line can be observed in the emission spectrum, and the condition of the dark line is given. We found that the conversion between destructive and constructive quantum interference can be achieved through controlling the Rabi frequency of the external fields.

Correction to "Charge Recombination Suppressed by Destructive Quantum Interference in Heterojunction Materials".

Correction to "Charge Recombination Suppressed by Destructive Quantum Interference in Heterojunction Materials".

Raman study of the quantum interference of multiple discrete states and a continuum of states in the phonon energy region of semiconductors: examples of p-type Ga0.5In0.5P films

Although the Fano quantum interference of one longitudinal optical (LO) phonon mode and one electronic continuum of states due to inter-valence band transition has been investigated by the Raman spectra, there is no observation of the interference of multiple phonon modes despite its potential for electromagnetically induced transparency in the far infrared region. In this study, p-type Ga0.5In0.5P films with two main LO modes in the same plane of atomic vibration and one more mode due to CuPt-type ordering are investigated. Asymmetric line profiles, peak energy shifts and peak broadenings in the Raman spectra are analyzed, and the destructive quantum interference of these LO-continuum systems are observed. Discussion with the reference data of p-type GaAs and Si for the one-LO mode system reveals that the asymmetry parameter features the derivatives of the density of the continuum of states in the vicinity of the LO phonon energies and the degree of the electric polarization. It is found experimentally that the interaction between the two main LO modes through the interactions with the continuum states takes place. A1(LO) mode due to the ordering affects the spectrum, however the interaction with the main two LO modes through the continuum is small. On the basis of the experimental result, the spectrum features for this alloy with greater hole density are estimated, where the various controls of the absorption spectrum in the phonon energy region are predicted.

Mechanically controlled quantum interference in individual π-stacked dimers.

Recent observations of destructive quantum interference in single-molecule junctions confirm the role of quantum effects in the electronic conductance properties of molecular systems. These effects are central to a broad range of chemical and biological processes and may be beneficial for the design of single-molecule electronic components to exploit the intrinsic quantum effects that occur at the molecular scale. Here we show that destructive interference can be turned on or off within the same molecular system by mechanically controlling its conformation. Using a combination of ab initio calculations and single-molecule conductance measurements, we demonstrate the existence of a quasiperiodic destructive quantum-interference pattern along the breaking traces of π-stacked molecular dimers. The results demonstrate that it is possible to control the molecular conductance over more than one order of magnitude and with a sub-ångström resolution by exploiting the subtle structure-property relationship of π-stacked dimers.

Ramsey-type phase control of free-electron beams

Interference between multiple distinct paths is a defining property of quantum physics, where "paths" may involve actual physical trajectories, as in interferometry, or transitions between different internal (e.g. spin) states, or both. A hallmark of quantum coherent evolution is the possibility to interact with a system multiple times in a phase-preserving manner. This principle underpins powerful multi-dimensional optical and nuclear magnetic resonance spectroscopies and related techniques, including Ramsey's method of separated oscillatory fields used in atomic clocks. Previously established for atomic, molecular and quantum dot systems, recent developments in the optical quantum state preparation of free electron beams suggest a transfer of such concepts to the realm of ultrafast electron imaging and spectroscopy. Here, we demonstrate the sequential coherent interaction of free electron states with two spatially separated, phase-controlled optical near-fields. Ultrashort electron pulses are acted upon in a tailored nanostructure featuring two near-field regions with anisotropic polarization response. The amplitude and relative phase of these two near-fields are independently controlled by the incident polarization state, allowing for constructive and destructive quantum interference of the subsequent interactions. Future implementations of such electron-light interferometers may yield unprecedented access to optically phase-resolved electronic dynamics and dephasing mechanisms with attosecond precision.

Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs.

One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution.

Force sensing based on coherent quantum noise cancellation in a hybrid optomechanical cavity with squeezed-vacuum injection

We propose and analyse a feasible experimental scheme for a quantum force sensor based on the elimination of backaction noise through coherent quantum noise cancellation (CQNC) in a hybrid atom-cavity optomechanical setup assisted with squeezed vacuum injection. The force detector, which allows for a continuous, broadband detection of weak forces well below the standard quantum limit (SQL), is formed by a single optical cavity simultaneously coupled to a mechanical oscillator and to an ensemble of ultracold atoms. The latter acts as a negative-mass oscillator so that atomic noise exactly cancels the backaction noise from the mechanical oscillator due to destructive quantum interference. Squeezed vacuum injection enforces this cancellation and allows sub-SQL sensitivity to be reached in a very wide frequency band, and at much lower input laser powers.

Quantum Interference in the Vibrational Relaxation of the O-H Stretch Overtone of Liquid H2O.

Using femtosecond two-color infrared pump-probe spectroscopy, we study the vibrational relaxation of the O-H stretch vibrations of liquid H2O after excitation of the overtone transition. The overtone transition has its maximum at 6900 cm(-1) (1.45 μm), which is a relatively high frequency in view of the central frequency of 3400 cm(-1) of the fundamental transition. The excitation of the overtone leads to a transient induced absorption of two-exciton states of the O-H stretch vibrations. When the overtone excitation frequency is tuned from 6600 to 7200 cm(-1), the vibrational relaxation time constant of the two-exciton states increases from 400 ± 50 fs to 540 ± 40 fs. These values define a limited range of relatively long relaxation time constants compared to the range of relaxation time constants of 250-550 fs that we recently observed for the one-exciton O-H stretch vibrational state of liquid H2O ( S. T. van der Post et al., Nature Comm. 2015 , 6 , 8384 ). We explain the high central frequency and the limited range of relatively long relaxation time constants of the overtone transition from the destructive quantum interference of the mechanical and electrical anharmonic contributions to the overtone transition probability. As a result of this destructive interference, the overtone transition of liquid H2O is dominated by molecules of which the O-H groups donate relatively weak hydrogen bonds to other H2O molecules.

Tuning Conductance in Aromatic Molecules: Constructive and Counteractive Substituent Effects

Destructive quantum interference in aromatic hydrocarbons can be tuned using chemical substituents; however, classical chemical intuition is not enough to explain the effects on electron transport. Using Huckel theory and density functional theory calculations, in combination with the Landauer–Buttiker approach for charge transport, novel substituent effects are demonstrated. For a 1,3-linked benzene, an electron acceptor in position 2 is shown to have the same effect on the antiresonance energy as an electron donor in position 4 and vice versa. Substituents in position 5 have no effect on the antiresonance energy. The effects appear to be additive, such that a donor in position 2 will counteract a donor in position 4, leading to cancellation of the substituent effect. Counter- and nonactive substituent positions exist for all aromatic hydrocarbons and can be predicted using a diagrammatic approach. This insight should be useful when substituents are to be used for tuning destructive quantum interference ...

Influence of phonon reservoir on photon blockade in a driven quantum dot-cavity system

We theoretically investigate the influence of the phonon bath on photon blockade in a simultaneously driven dot-cavity system. An optimal condition for avoiding two-photon excitation of a cavity field is put forward which can be achieved by modulating the phase difference and the strengths of the driving fields. The second-order correlation function and the mean photon number of the cavity field are discussed. In the absence of phonon effect, the strong photon blockade in a moderate quantum dot (QD)-cavity coupling regime occurs, which can be attributed to the destructive quantum interference arisen from different transition paths induced by simultaneously driving the dressed QD-cavity system. The participation of acoustic-phonon reservoir produces new transition channels for the QD-cavity system, which leads to the damage of destructive interference. As a result, the photon blockade effect is hindered when taking the electron-phonon interaction into account. It is also found that the temperature of the phonon reservoir is disadvantageous for the generation of photon blockade.

Nonreciprocal conversion between microwave and optical photons in electro-optomechanical systems

We propose to demonstrate nonreciprocal conversion between microwave and optical photons in an electro-optomechanical system where a microwave mode and an optical mode are coupled indirectly via two non-degenerate mechanical modes. The nonreciprocal conversion is obtained in the broken time-reversal symmetry regime, where the conversion of photons from one frequency to the other is enhanced for constructive quantum interference while the conversion in the reversal direction is suppressed due to destructive quantum interference. It is interesting that the nonreciprocal response between the microwave and optical modes in the electro-optomechanical system appears at two different frequencies with opposite directions. The proposal can be used to realize nonreciprocal conversion between photons of any two distinctive modes with different frequencies. Moreover, the electro-optomechanical system can also be used to construct a three-port circulator for three optical modes with distinctively different frequencies by adding an auxiliary optical mode coupled to one of the mechanical modes.

Long-lived states with well-defined spins inspin−1/2homogeneous Bose gases

Many-body eigenfunctions of the total spin operator can be constructed from the spin and spatial wavefunctions with non-trivial permutation symmetries. Spin-dependent interactions can lead to relaxation of the spin eigenstates to the thermal equilibrium. A mechanism that stabilizes the many-body entangled states is proposed here. Surprisingly, in spite coupling with the chaotic motion of the spatial degrees of freedom, the spin relaxation can be suppressed by destructive quantum interference due to spherical vector and tensor terms of the spin-dependent interactions. Tuning the scattering lengths by the method of Feshbach resonances, readily available in cold atomic labs, can enhance the relaxation timescales by several orders of magnitude.

Close relation between quantum interference in molecular conductance and diradical existence

An empirical observation of a relationship between a striking feature of electronic transmission through a π-system, destructive quantum interference (QI), on one hand, and the stability of diradicals on the other, leads to the proof of a general theorem that relates the two. Subject to a number of simplifying assumptions, in a π-electron system, QI occurs when electrodes are attached to those positions of an N-carbon atom N-electron closed-shell hydrocarbon where the matrix elements of the Green's function vanish. These zeros come in two types, which are called easy and hard. Suppose an N+2 atom, N+2 electron hydrocarbon is formed by substituting 2 CH2 groups at two atoms, where the electrodes were. Then, if a QI feature is associated with electrode attachment to the two atoms of the original N atom system, the resulting augmented N+2 molecule will be a diradical. If there is no QI feature, i.e., transmission of current is normal if electrodes are attached to the two atoms, the resulting hydrocarbon will not be a diradical but will have a classical closed-shell electronic structure. Moreover, where a diradical exists, the easy zero is associated with a nondisjoint diradical, and the hard zero is associated with a disjoint one. A related theorem is proven for deletion of two sites from a hydrocarbon.

Plasmon induced transparency in the trimer of gold nanorods

The localized surface plasmon resonance can be generated on the surface of the nano-metamaterial by the interaction between the nano-metamaterial and the light field, and also many plasmon oscillation modes can occur in the process of the hybridization between many infinitesimal composite structures, which is widely used for adjusting the resonant frequency in the optical frequency domain. Recently, analogue of the electromagnetically induced transparency（EIT) has been realized in the low-loss nano-metamaterial, and is well known as the plasmon induced transparency（PIT). In atomic physics, EIT is an effect which originates from the destructive quantum interference of two different excitation pathways. A sharp dip of nearly ideal transmission can arise within the broad absorption profile, which indicates that the EIT can be used in the fields of slow slight, delay lines and low-loss metamaterial. In this paper, a trimer consisting of a vertical nanorod（serving as a dipole antenna) and two parallel nanorods（used as a quadrupole antenna) is employed to investigate the process mechanism of the PIT in detail. It is found that the vertical nanorod with a large broad linewidth can be strongly coupled with the light. However, the parallel nanorods are weakly coupled with the light and their narrow linewidths are almost from the intrinsic metal loss（Drude damping) that is much smaller than the radiative damping of the dipole antenna. These two antennas can be strongly coupled due to their close similarities. Moreover, the absorption spectra of the trimer obtained by using three-dimensional finite element method vary with its coupling distance and geometry size, and the dipole bright mode corresponding to the dipole antenna splits under the action of the dark mode for the quadrupole antenna. Thus, a fresh physical interpretation is given:the PIT is mainly due to the coherent superposition after the splitting of the dipole oscillation mode in the vertical nanorod, rather than the parallel nanorods. Taking into consideration the phase correlation associated with coupling process of two oscillators, we introduce a modified Lorentzian oscillator model to investigate the effects of the coupling phase factor on the modulation of the absorption spectra and the coherent superposition between the splitting bright modes on the PIT. These findings will provide theoretical references for the applications of artificial atom, optical switching and slow light devices designed in the nanosize range.

Charge Recombination Suppressed by Destructive Quantum Interference in Heterojunction Materials.

We show that charge recombination in ordered heterojunctions depends sensitively on the degree of coherent delocalization of charges at the donor-acceptor interface. Depending on the relative sign of the electron and hole transfer integrals, such delocalization can dramatically suppress recombination through destructive quantum interference. This could explain why measured recombination rates are significantly lower than predictions based on Langevin theory for a variety of organic bulk heterojunctions. Moreover, it opens up a design strategy for photovoltaic devices with enhanced efficiencies through coherently suppressed charge recombination.

Cold spots in quantum systems far from equilibrium: Local entropies and temperatures near absolute zero

We consider a question motivated by the third law of thermodynamics: can there be a local temperature arbitrarily close to absolute zero in a nonequilibrium quantum system? We consider nanoscale quantum conductors with the source reservoir held at finite temperature and the drain held at or near absolute zero, a problem outside the scope of linear response theory. We obtain local temperatures close to absolute zero when electrons originating from the finite temperature reservoir undergo destructive quantum interference. The local temperature is computed by numerically solving a nonlinear system of equations describing equilibration of a scanning thermoelectric probe with the system, and we obtain excellent agreement with analytic results derived using the Sommerfeld expansion. A local entropy for a nonequilibrium quantum system is introduced, and used as a metric quantifying the departure from local equilibrium. It is shown that the local entropy of the system tends to zero when the probe temperature tends to zero, consistent with the third law of thermodynamics.

Classes of two-photon states defined by linear interactions and destructive two-photon quantum interference in a single mode

We describe a two-photon quantum interference effect which differs from the Hong-Ou-Mandel effect in that the destructive quantum inference occurs on a component of the state where two photons are in a single output mode while maintaining the two-photon events in the alternative mode. This effect is manifestly nonclassical but requires more sophisticated technology to observe than the Hong-Ou-Mandel effect. The theory outlined in this paper can also be used to classify two-photon states into classes which are related by the ability to transform the states within the class by using only linear optical interactions. This theory shows that there is an infinite number of these classes of two photon states when there are two or more modes which can support the photons.

Illusory Connection between Cross-Conjugation and Quantum Interference

Quantum interference, be it destructive or constructive, has a substantial influence on the magnitude of molecular conductance, and consequently there is significant interest in predicting these effects. It is commonly thought that cross-conjugated paths result in suppressed conductance due to destructive quantum interference. Using Huckel theory and density functional theory calculations we investigate systems that break this cross-conjugation rule of thumb. We predict and rationalize how a class of conjugated molecules containing closed loops can exhibit destructive interference despite being linearly conjugated and exhibit constructive interference despite being cross-conjugated. The arguments build on the graphical rules derived by Markussen et al. [Nano Lett. 2010, 10, 4260] and the hitherto neglected effects of closed loops in the molecular structure. Furthermore, we identify the 1,3 connected azulene molecule as belonging to the closed-loop class and argue that this explains recent measurements of ...

Photoassisted transport in silicon dangling bond wires

We theoretically investigate charge transport through dangling bond (DB) nanostructures built on a passivated silicon (100) surface by selectively removing hydrogen atoms. We focus on dangling bond wires and on T-junctions. In the latter case, destructive quantum interference effects lead to a strong suppression of charge transport mediated by the DB electronic states. We demonstrate, however, that by applying a time periodic voltage, mimicking irradiation with monochromatic light, a dramatic enhancement of the current up to the μA range can be achieved. This result is however limited by the restriction on the AC field strength and frequency that bulk states should minimally contribute to charge transport; otherwise current leakage will set in. Despite this constraint, transconductance values of the order of 10−6 A/V can be achieved, illustrating the potential of the discussed systems to find applications in nanoscale electronics.

Quantum nonlinear cavity quantum electrodynamics with coherently prepared atoms

We propose a method to study the quantum nonlinearity and observe the multiphoton transitions in a multiatom CQED system. We show that by inducing simultaneously destructive quantum interference for the single-photon and two-photon excitations in the CQED system, it is possible to observe the direct three-photon excitation of the higher-order ladder states of the CQED system. We report an experiment with cold Rb atoms confined in an optical cavity and demonstrate such interference control of the multi-photon excitations of the CQED system. The observed nonlinear excitation of the CQED ladder states agrees with a theoretical analysis based on a fully quantized treatment of the CQED system, but disagrees with the semiclassical analysis of the CQED system. Thus it represents the first direct observation of the quantum nature of the multiatom CQED system and opens new ways to explore quantum nonlinearity and its applications in quantum optical systems in which multiple absorbers/emitters are coupled with photons in confined cavity structures.