Solid-state Environment Research Articles

Decoherence of Flux Qubits under Sub-Ohmic Bath

In two-level approximation, we investigate the influence of mutual inductive coupling in superconducting quantum circuits on the decoherence of flux qubits under sub-Ohmic thermal bath environment by utilizing Bloch-Redfield function. The investigation results show: (1) The memory effect existing in the solid-state environment is beneficial to prolong the decoherence time of the superconducting flux qubit, building sub-Ohmic thermal bath environments can improve the decoherence of the solid-state qubit. (2) When the quantum system and the thermal bath are in weak coupling, generally speaking, the mutual coupling effect between circuit elements will destroy the quantum coherence; but when the quantum system and the thermal bath are in strong coupling, it will help to enhance the decoherence time by controlling the mutual inductive coupling between the loop components.

Model of the Optical Emission of a Driven Semiconductor Quantum Dot: Phonon-Enhanced Coherent Scattering and Off-Resonant Sideband Narrowing

We study the crucial role played by the solid-state environment in determining the photon emission characteristics of a driven quantum dot. For resonant driving, we predict a phonon enhancement of the coherently emitted radiation field with increasing driving strength, in stark contrast to the conventional expectation of a rapidly decreasing fraction of coherent emission with stronger driving. This surprising behavior results from thermalization of the dot with respect to the phonon bath and leads to a nonstandard regime of resonance fluorescence in which significant coherent scattering and the Mollow triplet coexist. Off resonance, we show that despite the phonon influence, narrowing of dot spectral sideband widths can occur in certain regimes, consistent with an experimental trend.

In situ Seamless Magnetic Measurements for Solid‐State Electrochemical Processes in Prussian Blue Analogues

Seamless observation: Magnetic measurements in a solid-state electrochemical environment have been developed and applied to a mixed-valent chromium Prussian blue analogue (PBA) ferrimagnet. Battery cells containing PBA as a cathode active material were inserted into a SQUID and the PBA reduction during battery discharge was controlled. Magnetic changes were revealed that can be understood by the redox-induced spin changes of the Cr ions.

Collective light emission revisited: reservoir induced coherence.

We study the collective emission of a few emitters (up to three) in a cavity. In addition to the radiation coupling responsible for sub- and superradiance, we investigate emitters additionally coupled through a joint carrier reservoir. For such emitters, typically embedded in a solid state environment, the carrier reservoir provides a continuous pumping mechanism for the steady state emission. We show that the statistical properties of the emitted light depend strongly on the interaction between the emitters and the reservoir. Unexpectedly, the presence of the reservoir enhances the coherence of the emitted light already for a few emitters. This results from the fact that the carrier reservoir introduces new many-body correlations to the electronic transition and in this way suppresses multiphoton processes.

The role of phonon scattering in the indistinguishability of photons emitted from semiconductor cavity QED systems

A solid-state single-photon source emitting indistinguishable photons on-demand is an essential component of linear optics quantum computing schemes. However, the emitter will inevitably interact with the solid-state environment causing decoherence and loss of indistinguishability. In this paper, we present a comprehensive theoretical treatment of the influence of phonon scattering on the coherence properties of single photons emitted from semiconductor quantum dots. We model decoherence using a full microscopic theory and compare with standard Markovian approximations employing Lindblad-type relaxation terms. Significant differences between the two approaches are found.

Nitrogen-14 Nuclear Quadrupole Resonance Spectroscopy: A Promising Analytical Methodology for Medicines Authentication and Counterfeit Antimalarial Analysis

We report the detection and analysis of a suspected counterfeit sample of the antimalarial medicine Metakelfin through developing nitrogen-14 nuclear quadrupole resonance ((14)N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The (14)N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer. Metakelfin contains two active pharmaceutical ingredients, sulfalene and pyrimethamine, and NQR analysis revealed spectral differences for the sulfalene component indicative of differences in the processing history of the two batches. Furthermore, the NQR analysis provided quantitative information that the suspected counterfeit tablets contained only 43 ± 3%, as much sulfalene as the genuine Metakelfin tablets. Conversely, conventional nondestructive analysis by Fourier transform (FT)-Raman and FT-near infrared (NIR) spectroscopies only achieved differentiation between batches but no ascription. High performance liquid chromatography (HPLC)-UV analysis of the suspect tablets revealed a sulfalene content of 42 ± 2% of the labeled claim. The degree of agreement shows the promise of NQR as a means of the nondestructive identification and content-indicating first-stage analysis of counterfeit pharmaceuticals.

Diamond NV centers for quantum computing and quantum networks

Abstract

On the Biexponential Decay of the Photoluminescence of the Two Crystallographically-Independent Molecules in Crystals of [Cu(I)(phen)(PPh3)2][BF4

[Cu(I)(phen)(PPh3)2][BF4] crystallizes with two nonsymmetry-related molecules in the asymmetric unit. Synchrotron time-resolved X-ray diffraction experiments have shown that the two independent molecules distort differently on MLCT excitation. The luminescence decay of the crystals is biexponential with two different Stokes-shifts, the more rapid decay corresponding to the shorter wavelength emission. Its amplitude diminishes rapidly with an increase in temperature, indicating that this emission is not due to a thermal activation to a higher state. The double emission is attributed to the presence of two independent molecules with drastically different packing environments. It is concluded that the solid-state environment must be analyzed whenever photochemical properties of molecular solids are reported.

Structural interrogation of a cucurbit[7]uril-ferrocene host–guest complex in the solid state: a Raman spectroscopy study

A complex formed between cucurbit[7]uril (CB7) and ferrocene (Fc) is investigated in the solid state using Raman spectroscopy. The Raman spectra are compared with those of the CB7 host and the Fc guest reference molecules, revealing significant frequency shifts of some vibrational modes upon complexation. These changes expose the structural and electronic interactions between the host and guest components and provide evidence that the ferrocene moiety resides within the cucurbituril cavity in the solid state environment.

Temporal quantum control with graphene

We introduce a novel strategy for controlling the temporal evolution of a quantum system at the nanoscale. Our method relies on the use of graphene plasmons, which can be electrically tuned in frequency by external gates. Quantum emitters (e.g. quantum dots) placed in the vicinity of a graphene nanostructure are subject to a strong interaction with the plasmons of this material, thus undergoing time variations in their mutual interaction and quantum evolution that are dictated by the externally applied gating voltages. This scheme opens a new path towards the realization of quantum-optics devices in the robust solid-state environment of graphene.

Electron emission in laser-nanotip interaction

The interaction of ultrashort laser pulses with nano-scale metal tips provides a unique testing ground for strong-field physics in a confined solid state environment. We theoretically investigate the spectrum of emitted electrons, which is directly related to the quantum dynamics at the surface.

Creation of entangled states in coupled quantum dots via adiabatic rapid passage

Quantum state preparation through external control is fundamental to established methods in quantum information processing and in studies of dynamics. In this respect, excitons in semiconductor quantum dots are of particular interest, since their coupling to light allows them to be driven into a specified state using the coherent interaction with a tuned optical field, such as an external laser pulse. We propose a protocol, based on adiabatic rapid passage, for the creation of entangled states in an ensemble of pairwise coupled two-level systems, such as an ensemble of coupled quantum dots. We show by quantitative analysis using realistic parameters for semiconductor quantum dots that this method is feasible where other approaches are unavailable. Furthermore, this scheme can be generically transferred to some other physical systems, including circuit QED, nuclear and electron spins in solid-state environments, and photonic coupled cavities.

The influence of mutual inductance effect on the decoherence of the flux qubits under super-Ohm thermal reservoir environment

In two-level approximation, we studied the influence of the mutual inductive coupling in the superconducting quantum circuits on the decoherence of the flux qubits under super-Ohm thermal reservoir environment by utilizing Bloch–Redfield function. The results show: (1) the memory effect existing in the solid-state environment and the Ohmic thermal reservoir caused by the deformation potential will help to prolong the decoherence time of the superconducting flux qubit, building super-Ohm thermal reservoir environments will be the best candidate available for improving the decoherence of the solid-state qubit. (2) When the quantum system and the thermal reservoir environment are in weak coupling, generally speaking, the mutual coupling effect between circuit elements will destroy the quantum coherence; but when the quantum system and the thermal reservoir environment are in strong coupling, it will be beneficial to enhance the decoherence time by controlling the mutual inductive coupling between the loop components.

Influence of two-level fluctuators on adiabatic passage techniques

We study the process of stimulated Raman adiabatic passage (STIRAP) under the influence of a nontrivial solid-state environment, particularly the effect of two-level fluctuators (TLFs) as they are frequently present in solid-state devices. When the amplitudes of the driving pulses used in STIRAP are in resonance with the level spacing of the fluctuators, the quality of the protocol, i.e., the transferred population, decreases sharply. In general, the effect can not be reduced by speeding up the STIRAP process. We also discuss the effect of a structured noise environment on the process of coherent tunneling by adiabatic passage (CTAP). The effect of a weakly structured environment or TLFs with short coherence times on STIRAP and CTAP can be described by the Bloch-Redfield theory. For a strongly structured environment, a higher-dimensional approach must be used, where the TLFs are treated as part of the system.

Suppression of spin-bath dynamics for improved coherence of multi-spin-qubit systems

Multi-qubit systems are crucial for the advancement and application of quantum science. Such systems require maintaining long coherence times while increasing the number of qubits available for coherent manipulation. For solid-state spin systems, qubit coherence is closely related to fundamental questions of many-body spin dynamics. Here we apply a coherent spectroscopic technique to characterize the dynamics of the composite solid-state spin environment of nitrogen-vacancy colour centres in room temperature diamond. We identify a possible new mechanism in diamond for suppression of electronic spin-bath dynamics in the presence of a nuclear spin bath of sufficient concentration. This suppression enhances the efficacy of dynamical decoupling techniques, resulting in increased coherence times for multi-spin-qubit systems, thus paving the way for applications in quantum information, sensing and metrology.

Maxwell's demon based on a single-electron pump

We propose and analyze a possible implementation of Maxwell's demon (MD) based on a single-electron pump. It presents a practical realization of MD in a solid-state environment. We show that measurements of the charge states of the pump and feedback control of the gate voltages lead to a net flow of electrons against the bias voltage ideally with no work done on the system by the gate control. The information obtained in the measurements converts thermal fluctuations into energy stored in a capacitor. We derive the conditions on the detector back action and measurement time necessary for implementing this conversion.

High-dynamic-range magnetometry with a single electronic spin in diamond

Magnetic sensors capable of detecting nanoscale volumes of spins allow for non-invasive, element-specific probing. The error in such measurements is usually reduced by increasing the measurement time, and noise averaging the signal. However, achieving the best precision requires restricting the maximum possible field strength to much less than the spectral linewidth of the sensor. Quantum entanglement and squeezing can then be used to improve precision (although they are difficult to implement in solid-state environments). When the field strength is comparable to or greater than the spectral linewidth, an undesirable trade-off between field strength and signal precision occurs. Here, we implement novel phase estimation algorithms on a single electronic spin associated with the nitrogen-vacancy defect centre in diamond to achieve an ∼8.5-fold improvement in the ratio of the maximum field strength to precision, for field magnitudes that are large (∼0.3mT) compared to the spectral linewidth of the sensor (∼4.5µT). The field uncertainty in our approach scales as 1/T(0.88), compared to 1/T(0.5) in the standard measurement approach, where T is the measurement time. Quantum phase estimation algorithms have also recently been implemented using a single nuclear spin in a nitrogen-vacancy centre. Besides their direct impact on applications in magnetic sensing and imaging at the nanoscale, these results may prove useful in improving a variety of high-precision spectroscopy techniques.

Dipotassium sodium niobium dioxide tetrafluoride, K 2NaNbO 2F 4, crystal structure and characterization

The paper presents a new data on the crystal structure of K 2NaNbO 2F 4. Single crystals of K 2NaNbO 2F 4, were obtained from the system of KF–NaF–Nb 2O 5. The compound is cubic, space group Fm3̄ m (No. 225), and the unit cell parameters are a=8.4726(4) Å, Z=4, Volume=608.21(5) Å 3. The structure was solved by the direct methods and refined to the reliability factors R 1=0.0116 ( wR 2=0.0302). Its structure can be described as three-dimensional frameworks formed of (0 1 0) [Na 2Nb 2O 4F 8]∞ layers stacked along b axis. In the framework, niobium, oxygen, fluorine atoms form a rare [NbO 2F 4] 3− anion group in an anhydrous solid state environment. The IR spectrum further confirmed the presence of NbO 2 and NbF 4 groups in the structure. The thermal analysis suggests that K 2NaNbO 2F 4 is an incongruently melting compound.

Decoherence times of universal two-qubit gates in the presence of broad-band noise

The controlled generation of entangled states of two quantum bits is a fundamental step toward the implementation of a quantum information processor. In nano-devices this operation is counteracted by the solid-state environment, characterized by a broadband and non-monotonic power spectrum, often 1/f, at low frequencies. For single-qubit gates, incoherent processes due to fluctuations acting on different time scales result in peculiar short- and long-time behavior. Markovian noise gives rise to exponential decay with relaxation and decoherence times, T1 and T2, simply related to the symmetry of the qubit–environment coupling Hamiltonian. Noise with the 1/f power spectrum at low frequencies is instead responsible for defocusing processes and algebraic short-time behavior. In this paper, we identify the relevant decoherence times of an entangling operation due to the different decoherence channels originating from solid-state noise. Entanglement is quantified by concurrence, which we evaluate in an analytic form employing a multi-stage approach. The ‘optimal’ operating conditions of reduced sensitivity to noise sources are identified. We apply this analysis to a superconducting gate for experimental noise spectra.

High-resolution electrical detection of free induction decay and Hahn echoes in phosphorus-doped silicon

Paramagnetic centers in a solid-state environment usually give rise to inhomogenously broadened electron paramagnetic resonance (EPR) lines, making conventionally detected free induction decay (FID) signals disappear within the spectrometer dead time. Here, experimental results of an electrically detected FID of phosphorus donors in silicon epilayers with natural isotope composition are presented, showing Ramsey fringes within the first 150 ns. An analytical model is developed to account for the data obtained as well as for the results of analogous two-pulse echo experiments. The results of a numerical calculation are further presented to assess the capability of the method to study spin-spin interactions.