Coherent Microwave Field Research Articles

Coherent memory for microwave photons based on long-lived mechanical excitations

Mechanical resonators, due to their capability to host ultralong-lived phonon modes, are particularly attractive for quantum state storage and as memory elements in conjunction with quantum computing and communication networks. Here we demonstrate absorptive-type coherent memory based on long-lived mechanical excitations. The itinerant coherent microwave field is captured, stored, and retrieved from a mechanical memory oscillator which is pre-cooled to the ground state. The phase space distribution allows us to distinguish between coherent and thermal components and study their evolution as a function of storage time. Our device exhibits attractive functions with an energy decay time of T1 = 15.9 s, a thermal decoherence rate of Γth = 2.85 Hz, and acquires less than one quantum noise during the τcoh = 55.7 ms storage period. We demonstrate that both the amplitude and phase information of microwave coherent states can be recovered, indicating the coherence of our memory device. These results suggest that high-Q mechanical resonators and long coherence time phonons could be ideal candidates for the construction of long-lived and on-demand microwave quantum memories.

A quantum model of lasing without inversion

Starting from a quantum description of multiple Λ-type three-level atoms driven with a coherent microwave field and incoherent optical pumping, we derive a microscopic model of lasing from which we move towards a consistent macroscopic picture. Our analysis applies across the range of system sizes from nanolasers to the thermodynamic limit of conventional lasing. We explore the necessary conditions to achieve lasing without inversion in certain regimes by calculating the non-equilibrium steady state solutions of the model at, and between, its microscopic and macroscopic limits. For the macroscopic picture, we use mean-field theory to present a thorough analysis of the lasing phase transition. In the microscopic case, we exploit the underlying permutation symmetry of the density matrix to calculate exact solutions for N three-level systems. This allows us to show that the steady state solutions approach the thermodynamic limit as N increases, restoring the sharp non-equilibrium phase transition in this limit. We demonstrate how the lasing phase transition and degree of population inversion can be adjusted by simply varying the phase of the coherent driving field. The high level of quantum control presented by this microscopic model and the framework outlined here have applications to further understanding and developing nanophotonic technology.

Chip-to-chip entanglement of transmon qubits using engineered measurement fields

While the on-chip processing power in circuit QED devices is growing rapidly, an open challenge is to establish high-fidelity quantum links between qubits on different chips. Here, we show entanglement between transmon qubits on different cQED chips with $49\%$ concurrence and $73\%$ Bell-state fidelity. We engineer a half-parity measurement by successively reflecting a coherent microwave field off two nearly-identical transmon-resonator systems. By ensuring the measured output field does not distinguish $\vert 01 \rangle$ from $\vert 10 \rangle$, unentangled superposition states are probabilistically projected onto entangled states in the odd-parity subspace. We use in-situ tunability and an additional weakly coupled driving field on the second resonator to overcome imperfect matching due to fabrication variations. To demonstrate the flexibility of this approach, we also produce an even-parity entangled state of similar quality, by engineering the matching of outputs for the $\vert 00 \rangle$ and $\vert 11 \rangle$ states. The protocol is characterized over a range of measurement strengths using quantum state tomography showing good agreement with a comprehensive theoretical model.

Magnon-mediated spin current noise in ferromagnet|nonmagnetic conductor hybrids

The quantum excitations of the collective magnetization dynamics in a ferromagnet (F) - magnons - enable spin transport without an associated charge current. This pure spin current can be transferred to electrons in an adjacent non-magnetic conductor (N). We evaluate the finite temperature noise of the magnon-mediated spin current injected into N by an adjacent F driven by a coherent microwave field. We find that the dipolar interaction leads to squeezing of the magnon modes giving them wavevector dependent non-integral spin, which directly manifests itself in the shot noise. For temperatures higher than the magnon gap, the thermal noise is dominated by large wavevector magnons which exhibit negligible squeezing. The noise spectrum is white up to the frequency corresponding to the maximum of the temperature or the magnon gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The shot noise is found to be much larger than its thermal counterpart over a broad temperature range, making the former easier to be measured experimentally.

Detection of a weak magnetic field via cavity-enhanced Faraday rotation

We study the sensitive detection of a weak static magnetic field via Faraday rotation induced by an ensemble of spins in a bimodal degenerate microwave cavity. We determine the limit of the resolution for the sensitivity of the magnetometry achieved using either single-photon or multiphoton inputs. For the case of a microwave cavity containing an ensemble of Nitrogen-vacancy defects in diamond, we obtain a magnetometry sensitivity exceeding $0.5~\text{\nano\tesla}/\sqrt{\text{\hertz}}$, utilizing a single photon probe field, while for a multiphoton input we achieve a sensitivity about $1 \text{\femto\tesla}/\sqrt{\text{\hertz}}$, using a coherent probe microwave field with power of $P_\text{in}=1~\text{\nano\watt}$.

Squeezing with a flux-driven Josephson parametric amplifier

Josephson parametric amplifiers (JPA) are promising devices for applications in circuit quantum electrodynamics and for studies on propagating quantum microwaves because of their good noise performance. In this work, we present a systematic characterization of a flux-driven JPA at millikelvin temperatures. In particular, we study in detail its squeezing properties by two different detection techniques. With the homodyne setup, we observe the squeezing of vacuum fluctuations by superposing signal and idler bands. For a quantitative analysis, we apply dual-path cross-correlation techniques to reconstruct the Wigner functions of various squeezed vacuum and thermal states. At 10 dB signal gain, we find 4.9 ± 0.2 dB squeezing below the vacuum. In addition, we discuss the physics behind squeezed coherent microwave fields. Finally, we analyze the JPA noise temperature in the degenerate mode and find a value smaller than the standard quantum limit for phase-insensitive amplifiers.

Giant Cross–Kerr Effect for Propagating Microwaves Induced by an Artificial Atom

We investigate the effective interaction between two microwave fields, mediated by a transmon-type superconducting artificial atom which is strongly coupled to a coplanar transmission line. The interaction between the fields and atom produces an effective cross-Kerr coupling. We demonstrate average cross-Kerr phase shifts of up to 20 degrees per photon with both coherent microwave fields at the single-photon level. Our results provide an important step toward quantum applications with propagating microwave photons.

Electromagnetic-field-induced decay of currents in superconducting thin-film rings with photon emission

It is shown that superconducting currents in thin-film rings irradiated by coherent microwave field can decay with emission of photons. When the ring thickness is less than the field penetration depth, the field induces coherent oscillations of all the Cooper pairs in the ring. The oscillating condensate will emit photons with energies determined by the difference of quantized energy levels of the superconducting ring. The probability of the microwave field-induced single-photon decay of the supercurrents is calculated. The angular distributions of the photons emitted by the superconducting rings and the lifetimes of the current states, depending on both the ring sizes and the fluxoid numbers in the initial states, are studied.

Observation of Autler-Townes Effect in Electromagnetically Induced Transparency

We report an experimental observation of Autler-Townes doublet splitting in electromagnetically induced transparency (EIT) resonance. The splitting is introduced by a coherent microwave field, which perturbs a three-level A-type EIT system through an auxiliary level. The doublet splitting of EIT resonance is demonstrated in two cases, where the microwave field shares a common lower level with coupled or probe transition, respectively. The dependence of doublet splitting on microwave field intensity and detuning is measured. This may provide a feasible way of manipulating the atomic states with both laser and microwave field.

Field and dipole squeezing in a driven degenerate Λ quantum-beat system

Abstract The properties of field squeezing and atomic dipole squeezing in a coherent-microwave field driven degenerate Λ quantum-beat system were theoretically investigated. Numerical calculations indicate that the driving microwave may enhance or suppress both dipole squeezing and cavity-field squeezing, depending on the atomic energy level splitting and the microwave Rabi frequency.

Chaotic ionization of non-classical alkali Rydberg states—computational physics beats experiment

We report on a novel numerical treatment of highly excited alkali Rydberg states strongly driven by a coherent microwave field. Our approach establishes particularly clean experimental conditions which remain to be realized by the traditional experimentalist in the laboratory. First results obtained on the largest currently available parallel supercomputers resolve a long-standing problem in the theoretical analysis of the ionization process of nonhydrogenic alkali Rydberg states.

A Possible Pumping Mechanism for Interstellar Class II 107 GHz Methanol Masers

It is recognized that the interstellar methanol-107 GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pumping mechanism–methanol masers without population inversion. It can explain the formation of 107 GHz methanol masers, with the 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.

Coherent control of optical gain from electronic intersubband transitions in semiconductors

We study electronic transitions between a subband and a lower subband doublet which is driven by a coherent microwave (MW) field in a semiconductor double well structure. Within a microscopic three-band model, we show that variation of the MW phase allows manipulation of the optical gain provided the probe pulse duration is shorter than the period of the MW-field-generated interband polarization in the doublet. Moreover, we find that optical gain without inversion can be achieved in spite of subpicosecond dissipative mechanisms provided by electron-phonon coupling and electron tunneling into and out of the double well.

Maser action without inversion in interstellar space

It is recognized that interstellar 6.7 and 12.2 GHz methanol masers toward Class II sources are associated with each other and coexist toward ultracompact HII regions. Therefore we suggest a new excitation mechanism – methanol masers without population inversion. This mechanism can explain the formation of 6.7 GHz methanol masers while the 12.2 GHz methanol masers are regarded as driving coherent microwave fields. It is discussed that this mechanism is associated with astronomical conditions.

Coherent Control of Light Absorption and Carrier Dynamics in Semiconductor Nanostructures

It is shown theoretically that light absorption in semiconductor nanostructures can be manipulated by coherent microwave fields. In suitably designed double wells, amplitude and phase of a microwave field allow control of both light absorption and the dynamics, i.e., tunneling versus localization of electrons. Depending on the photon energy of the pump pulse, either enhancement or reduction of net absorption can be achieved.

Optical Nutation Effect in the Three-Level System Driven by a Coherent Microwave Field

In this paper, a coherent transient effect–optical nutation in Bloch form is studied semiclassically in the three-level atomic system driven by a coherent microwave field. The amplitude of the optical nutation signal field is obtained. It is found that the signal field, related to the microwave, is the overlap of two slow oscillations instead of one.

Optical Free-Induction Decay Effect in a Λ-Type Quantum-Beat Three-Level System

With Bloch form, a coherent transient effect–optical free-induction decay is studied semiclassically in the Λ-type three-level system driven by a coherent microwave field. The decay behavior has three contributions: a homogeneous part with transverse relaxation time and two inhomogeneous parts with different time constants that reflect the velocity bandwidth excited and the action of the driving microwave field.

A RADIATION MECHANISM FOR INTERSTELLAR METHANOL 6.7GHZ MASERS

All interstellar methanol maser sources can be divided into two classes. Their spectra are distinctive. In particular, the prominent Class II maser transitions, 6.7GHz and 12.2GHz lines show enhanced absorption toward Class I sources. We notice that the 6.7 and 12.2GHz methanol masers toward Class II sources are associated with each other and coexist toward ultracompact HII regions. Therefore we suggest a new pumping mechanism – methanol masers without population inversion. It can be used to explain the formation of 6.7GHz methanol masers while the 12.2GHz methanol masers are regarded as driving coherent microwave field. In this paper, we demonstrate that the new mechanism is associated with astronomical conditions and does not contradict with other mechanisms.

From coherent to noise-induced microwave ionization of Rydberg atoms.

We present an experimental study of dynamical localization as displayed by rubidium Rydberg atoms ionized by a coherent microwave field. The ionization threshold field has been measured over a wide range of initial principal quantum numbers of the atomic Rydberg states, for a fixed interaction time of atom and field, and for two different values of the frequency of the microwave. Furthermore, fixing the initial state of the atoms and the microwave frequency, we studied the dependence of the ionization threshold on the interaction time. In both types of experiments, we identify a clear signature of dynamical localization and of its gradual destruction by noise. The transition from dynamical localization to diffusionlike ionization as weak broadband noise is added to the coherent microwave radiation is illustrated. In addition, we supply experimental evidence that suggests that a subset of the noise spectrum depending on the principal quantum number of the initial atomic Rydberg state is more relevant for the destruction of dynamical localization.

Microwave “ionization” of excited hydrogen atoms: How nonclassical local stability brought about by scarred separatrix states is affected by broadband noise and by varying the pulse envelope

Abstract Studies of the microwave “ionization” of excited hydrogen atoms have shonn (so far) six regimes of dynamical behavior as one changes the scaled frequency, which is the ratio of the driving frequency ω and the classical Kepler frequency ω k . After a brief description of each regime, we focus on the results of recent experiments probing the detailed semiclassical behavior in two of them. Observed nonclassical local stability that, nevertheless, classically scales has been explained theoretically as being brought about by scarred quantal wavefunctions anchored semiclassically to the (broken) separatrix regions in the classical phase space above and below the main nonlinear resonance zone centered near ω ω k = 1 1 . The experimental data show that the upper and lower separatrix states states are affected differently by broadband noise added to the coherent microwave field and by variations in the microwave pulse envelope. Implications of these results for future work are discussed.