Phase Flip Research Articles

Single-shot simulations of dynamics of quantum dark solitons

Eigenstates of Bose particles with repulsive contact interactions in one-dimensional space with periodic boundary conditions can be found with the help of the Bethe ansatz. The type~II excitation spectrum identified by E. H. Lieb, reproduces the dispersion relation of dark solitons in the mean-field approach. The corresponding eigenstates possess translational symmetry which can be broken in measurements of positions of particles. We analyze emergence of single and double solitons in the course of the measurements and investigate dynamics of the system. In the weak interaction limit, the system follows the mean-field prediction for a short period of time. Long time evolution reveals many-body effects that are related to an increasing uncertainty of soliton positions. In the strong interaction regime particles behave like impenetrable bosons. Then, the probability densities in the configuration space become identical to the probabilities of non-interacting fermions but the wave-functions themselves remember the original Bose statistics. Especially, the phase flips that are key signatures of the solitons in the weak interaction limit, can be observed in the time evolution of the strongly interacting bosons.

Severe stress hormone conditions cause an extended window of excitability in the mouse basolateral amygdala

Shortly after stress, basolateral amygdala neurons are exposed to sequential yet partly overlapping waves of hormones. We examined how these hormonal waves can change activity of basolateral amygdala neurons such that emotional aspects of stress become so deeply ingrained. To this end, spontaneous glutamatergic transmission was recorded during and up to several hours after combined adrenergic and corticosteroid waves, targeting the time-window relevant for encoding of stress-related information. Hormonal waves mimicking moderately stressful conditions cause a transient enhancement followed by later suppression of glutamatergic transmission. However, this late phase flips from suppressed to enhanced glutamatergic transmission with conditions mimicking severe stress. Such a prolonged window of enhanced excitability may contribute to the excessively strong encoding seen after the experience of highly stressful or traumatic events.

A photon-photon quantum gate based on a single atom in an optical resonator.

That two photons pass each other undisturbed in free space is ideal for the faithful transmission of information, but prohibits an interaction between the photons. Such an interaction is, however, required for a plethora of applications in optical quantum information processing. The long-standing challenge here is to realize a deterministic photon-photon gate, that is, a mutually controlled logic operation on the quantum states of the photons. This requires an interaction so strong that each of the two photons can shift the other's phase by π radians. For polarization qubits, this amounts to the conditional flipping of one photon's polarization to an orthogonal state. So far, only probabilistic gates based on linear optics and photon detectors have been realized, because "no known or foreseen material has an optical nonlinearity strong enough to implement this conditional phase shift''. Meanwhile, tremendous progress in the development of quantum-nonlinear systems has opened up new possibilities for single-photon experiments. Platforms range from Rydberg blockade in atomic ensembles to single-atom cavity quantum electrodynamics. Applications such as single-photon switches and transistors, two-photon gateways, nondestructive photon detectors, photon routers and nonlinear phase shifters have been demonstrated, but none of them with the ideal information carriers: optical qubits in discriminable modes. Here we use the strong light-matter coupling provided by a single atom in a high-finesse optical resonator to realize the Duan-Kimble protocol of a universal controlled phase flip (π phase shift) photon-photon quantum gate. We achieve an average gate fidelity of (76.2 ± 3.6) per cent and specifically demonstrate the capability of conditional polarization flipping as well as entanglement generation between independent input photons. This photon-photon quantum gate is a universal quantum logic element, and therefore could perform most existing two-photon operations. The demonstrated feasibility of deterministic protocols for the optical processing of quantum information could lead to new applications in which photons are essential, especially long-distance quantum communication and scalable quantum computing.

Location of the first plasma response to resonant magnetic perturbations in DIII-D H-mode plasmas

The resonant location of the first plasma response to periodic toroidal phase flips of a resonant magnetic perturbation (RMP) field is experimentally identified in the DIII-D tokamak using phase minima of the modulated plasma density and toroidal rotation relative to the RMP field. The plasma response coincides with the q = 3 rational surface and electron fluid velocity null, which is consistent with simulations of the plasma response to the RMP field from resistive magnetohydrodynamics (MHD) modeling. An asymmetric propagation of the particle and the momentum transport from the resonant location of the plasma response to the RMP into the core and into the plasma edge is observed.

Quantum noise on the coherent-transport protocol for clock synchronization

The paper presents the synchronization accuracies of the coherent-transport protocol in the presence of quantum noise. Under the influence of bit flip noise, the accuracy will reduce to the standard quantum limit. When influenced by phase flip and amplitude damping, the accuracies are lower than the standard quantum limit in most cases. By comparison to the performance of the onequbit transport protocol and the entangled-states transport protocol, we found the accuracy of the coherent-transport protocol to be lower than the accuracies of the other two protocols in the presence of phase flip and amplitude damping.

Teleportation of a ququart system using hyperentangled photons assisted by atomic-ensemble memories

A single photon encoded in both the spin and the orbital angular momentum has recently been experimentally demonstrated [X.-L. Wang et al., Nature 518, 516 (2015)] with linear optics using the hyperentangled state, which can be viewed as a bipartite four-dimensional (ququart) entanglement. Here, we investigate this process from a general point of view. By exploring a controlled phase flip induced by atomic ensembles in one-side optical microcavities, we propose teleportations of general ququart systems including a two-atomic-ensemble system, a two-polarized-photon system, one photon with the polarization and spatial degrees of freedom (DOFs), and a hybrid photon-ensemble system using two hyperentangled photons. The output information may also be encoded by different physical systems up to the special requirements of a receiver. These schemes are also adapted to teleportation of a ququart system with only phases or real probability amplitudes, which is beyond previous superdense teleportation [Nature Commun. 6, 7185 (2015)]. With these restrictions, half of the classical communication cost may be saved and experimental complexities are also reduced. Our theoretical schemes are feasible in modern physics and show the possibilities of transferring complex quantum systems for scalable quantum applications.

Grover search with lackadaisical quantum walks

The lazy random walk, where the walker has some probability of staying put, is a useful tool in classical algorithms. We propose a quantum analogue, the lackadaisical quantum walk, where each vertex is given l self-loops, and we investigate its effects on Grover’s algorithm when formulated as search for a marked vertex on the complete graph of N vertices. For the discrete-time quantum walk using the phase flip coin, adding a self-loop to each vertex boosts the success probability from 1/2 to 1. Additional self-loops, however, decrease the success probability. Using instead the Shenvi, Kempe, and Whaley (2003) coin, adding self-loops simply slows down the search. These coins also differ in that the first is faster than classical when l scales less than N, while the second requires that l scale less than N2. Finally, continuous-time quantum walks differ from both of these discrete-time examples—the self-loops make no difference at all. These behaviors generalize to multiple marked vertices.

Single-photon entanglement purification procedure in a squeezed generalized amplitude damping channel

Analyzing the effects of the squeezed generalized amplitude damping noise on the single-photon entanglement purification procedure with path length fluctuations, we find that, for large value of T, the amplitude noise becomes as important as the phase flip noise in the role of origin of the discrepancy between the experimental value 0.796 of Salart et al. (Phys. Rev. Lett. 104 180504, 2010) and the theoretical value of 0.808 of Sangouard et al. (Phys. Rev. A 78 050301, 2008).

Fighting noise with noise in realistic quantum teleportation

We investigate how the efficiency of the quantum teleportation protocol is affected when the qubits involved in the protocol are subjected to noise or decoherence. We study all types of noise usually encountered in real world implementations of quantum communication protocols, namely, the bit flip, phase flip (phase damping), depolarizing, and amplitude damping noise. Several realistic scenarios are studied in which a part or all of the qubits employed in the execution of the quantum teleportation protocol are subjected to the same or different types of noise. We find noise scenarios not yet known in which more noise or less entanglement lead to more efficiency. Furthermore, we show that if noise is unavoidable it is better to subject the qubits to different noise channels in order to obtain an increase in the efficiency of the protocol.

On the quantum discord of general X states

Quantum discord Q is a function of density matrix elements. The domain of such a function in the case of two-qubit system with X density matrix may consist of three subdomains at most: two ones where the quantum discord is expressed in closed analytical forms (Q_{\pi/2} and Q_0) and an intermediate subdomain for which, to extract the quantum discord Q_\theta, it is required to solve in general numerically a one-dimensional minimization problem to find the optimal measurement angle \theta\in(0,\pi/2). Hence the quantum discord is given by a piecewise-analytic-numerical formula Q=\min{Q_{\pi/2}, Q_\theta, Q_0}. Equations for determining the boundaries between these subdomains are obtained. The boundaries consist of bifurcation points. The Q_{\theta} subdomains are discovered in the generalized Horodecki states, in the dynamical phase flip channel model, in the anisotropic spin systems at thermal equilibrium, in the heteronuclear dimers in an external magnetic field. We found that transitions between Q_{\theta} subdomain and Q_{\pi/2} and Q_0 ones occur suddenly but continuously and smoothly, i.e., nonanalyticity is hidden and can be observed in higher derivatives of discord function.

Quantum private comparison over noisy channels

Quantum Private Comparison (QPC) allows us to protect private information during its comparison. In the past various three-party quantum protocols have been proposed that claim to work well under noisy conditions. Here we tackle the problem of QPC under noise. We analyze the EPR-based protocol under depolarizing noise, bit flip and phase flip noise. We show how noise affects the robustness of the EPR-based protocol. We then present a straightforward protocol based on CSS codes to perform QPC which is robust against noise and secure under general attacks.

Parity-gate-based quantum information processing in decoherence-free subspace with nitrogen-vacancy centers

We propose a parity-check gate (PCG) for logical qubits encoded in decoherence-free subspace (DFS) by the coherent optical pulse input–output process with nitrogen-vacancy (NV) centers fixed on the surface of microtoroidal resonators (MTRs) with quantized whispering-gallery modes (WGMs). Using the proposed PCG, we achieve controlled phase flip (CPF) gate, |χ〉 state generation, and multipartite entanglement purification. The present schemes combine the advantages of the robustness of coherent pulse and the immunity to the dephasing noise of the DFS. The performances of these schemes are also analyzed, which shows that all the schemes works well in the low-Q cavity regime and are feasible under the current experimental technology.

Bipartite networks of oscillators with distributed delays: Synchronization branches and multistability.

We study synchronization in bipartite networks of phase oscillators with general nonlinear coupling and distributed time delays. Phase-locked solutions are shown to arise, where the oscillators in each partition are perfectly synchronized among themselves but can have a phase difference with the other partition, with the phase difference necessarily being either zero or π radians. Analytical conditions for the stability of both types of solutions are obtained and solution branches are explicitly calculated, revealing that the network can have several coexisting stable solutions. With increasing value of the mean delay, the system exhibits hysteresis, phase flips, final state sensitivity, and an extreme form of multistability where the numbers of stable in-phase and antiphase synchronous solutions with distinct frequencies grow without bound. The theory is applied to networks of Landau-Stuart and Rössler oscillators and shown to accurately predict both in-phase and antiphase synchronous behavior in appropriate parameter ranges.

Probabilistic cloning of a single-atom state via cavity QED

We propose a scheme for probabilistically cloning a two-level state of an atom to a polarization photon via cavity QED system combined with linear optics elements. By choosing appropriate parameters, a controlled phase flip (CPF) gate between the atom and the probe photon is realized. Then we can judge that the cloning process should be continued (with the optimal probability) or interrupted by detecting the probe photon. If the cloning can be continued, the original atom state is deterministically cloned to the cloning photon by performing two more CPF gates and three single-qubit unitary operations. Otherwise, if the detection shows that the cloning should be interrupted, the cloning photon and the relevant operations are omitted.

Efficient preparation of Greenberger–Horne–Zeilinger state and W state of atoms with the help of the controlled phase flip gates in quantum nodes connected by collective-noise channels

Noise plays a troublesome role for entanglement generation, because the polarization entanglement of photons can be easily disturbed by the noise. In this paper, we propose a protocol to prepare Greenberger–Horne–Zeilinger state and W state of atoms in quantum nodes connected by collective-noise channels assisted by quantum nondemolition detectors (QNDs) and the controlled phase flip gates. The frequency degrees of freedom are exploited in our protocol. The successful probability of our protocol can reach 100% neglecting the photon loss and assuming that the efficiency of QNDs is 1. Moreover, the number of times of using QNDs is limited, and this makes the protocol quite effective when collective noise is small.

Suppressing correlated noise in signals transmitted over the Gaussian memory channels using a2N-port splitter and phase flips

A scheme for suppressing the correlated noise in signals transmitted over the bosonic Gaussian memory channels is proposed. This is a compromise solution rather than removing the noise completely. The scheme is based on linear optical elements, two $N$-port splitters and $N$ number of phase flips. The proposed scheme has the advantages that the correlated noise of the memory channels is greatly suppressed, and the input signal states can be protected excellently when transmitting over the noise channels. We examine the suppressing efficiency of the scheme for the correlated noise, both from quantum information of the states directly transmitted through the noise channel and also from the entanglement teleportation. The operation of phase flips in our scheme is important for the suppression of the correlated noise, which can diminish the effect of noise in quantum communication. Increasing the number of beam splitters also can improve the suppressing efficiency of the scheme in quantum communication.

The Quantum Correlations of the Werner State Under Quantum Decoherence

This paper examines the quantum correlations of the Werner state and demonstrates the relationship between the quantum discord and entanglement under decoherence. We also identify that when the discord takes the maximal value for a given state, and discuss the boundary value for entanglement and discord. As we all know that, in an ideal environment, the quantum discord is always larger than the entanglement of formation for almost all entangled states. But, the analysis in the article exposes that the entanglement may show stronger anti-interference than quantum discord in the noisy channel. In addition, the emphasis is also placed on the problem of the relation between the geometric discord (D g ) and the entanglement of formation (EOF) which is customarily used as a measure of entanglement. At the same time, we also investigate the inequality 2D g ≥ N 2 and find that it is still be satisfied under the phase flip channel.

Refractometric biosensing based on optical phase flips in sparse and short-range-ordered nanoplasmonic layers

Noble metal nanoparticles support localized surface plasmon resonances (LSPRs) that are extremely sensitive to the local dielectric properties of the environment within distances up to 10–100 nm from the metal surface. The significant overlap between the sensing volume of the nanoparticles and the size of biological macromolecules has made LSPR biosensing a key field for the application of plasmonics. Recent advancements in evaluating plasmonic refractometric sensors have suggested that the phase detection of light can surpass the sensitivity of standard intensity-based detection techniques. Here, we experimentally confirm that the phase of light can be used to precisely track local refractive index changes induced by biomolecular reactions, even for dilute and layers of short-range-ordered plasmonic nanoparticles. In particular, we demonstrate that the sensitivity can be enhanced by tuning in to a zero reflection condition, in which an abrupt phase flip of the reflected light is achieved. Using a cost-effective interference fringe tracking technique, we demonstrate that phase measurements yield an approximately one order of magnitude larger relative shift compared with traditional LSPR measurements for the model system of NeutrAvidin binding to biotinylated nanodisks.

Assembling ellipsoidal particles at fluid interfaces using switchable dipolar capillary interactions.

How to dynamically tune an assembly of anisotropic colloidal particles adsorbed at fluid-fluid interfaces using dipolar capillary interactions is demonstrated. A previously discovered first-order phase transition is exploited and it is shown how to spontaneously turn off these dipolar capillary interactions by exceeding a critical field strength, providing unprecedented control of the bottom-up fabrication of soft materials.

Relative ordering of square-norm distance correlations in open quantum systems

We investigate the square-norm distance correlation dynamics of the Bell-diagonal states under different local decoherence channels, including phase flip, bit flip, and bit-phase flip channels by employing the geometric discord (GD) and its modified geometric discord (MGD), as the measures of the square-norm distance correlations. Moreover, an explicit comparison between them is made in detail. The results show that there is no distinct dominant relative ordering between them. Furthermore, we obtain that the GD just gradually deceases to zero, while MGD initially has a large freezing interval, and then suddenly changes in evolution. The longer the freezing interval, the less the MGD is. Interestingly, it is shown that the dynamic behaviors of the two geometric discords under the three noisy environments for the Werner-type initial states are the same.