Maser Cavity Research Articles

“Maser-in-a-shoebox”: A portable plug-and-play maser device at room temperature and zero magnetic field

Masers, the microwave analogs of lasers, have seen a renaissance owing to the discovery of gain media that mase at room temperature and zero-applied magnetic field. However, despite the ease with which the devices can be demonstrated under ambient conditions, achieving the ubiquity and portability, which lasers enjoy, has to date remained challenging. We present a maser device with a miniaturized maser cavity, gain material, and laser pump source that fits within the size of a shoebox. The gain medium used is pentacene-doped para-terphenyl, and it is shown to give a strong masing signal with a peak power of −5 dBm even within a smaller form factor. The device is also shown to mase at different frequencies within a small range of 1.5 MHz away from the resonant frequency. The portability and simplicity of the device, which weighs under 5 kg, paves the way for demonstrators particularly in the areas of low-noise amplifiers, quantum sensors, cavity quantum electrodynamics, and long-range communications.

Hydrogen maser magnetron cavity with low frequency-temperature coefficient

In this paper we show how a proper dimensioning of a magnetron cavity and its inner bulb allows one to design a hydrogen maser atomic clock with an arbitrary low frequency-temperature coefficient (FTC) for its cavity. The control of this parameter is of primary importance for the overall stability of the atomic clock. To this aim, a model based on finite element method has been developed to simulate thermal expansion of hydrogen maser cavities and evaluate the FTC. The model has been confronted with direct experimental data and very good agreement is observed. A key geometrical parameter is identified that allows for a strong tuning of the FTC, so as to set it down to values a priori as close as desired to 0, with limitations only dictated by the machining tolerances of the mechanical elements of the hydrogen maser cavity.

Enhanced magnetic Purcell effect in room-temperature masers.

Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation.

Quantum Tomography of Microwave Region

An alternative method of reconstruction of the density matrix of microwave range created in the maser cavity is proposed. Here a technique for measuring the probability density of the quadrature field for different phases is presented. The measured quantity is the probability of difference between the numbers of atoms emitted in the excited and ground states in a sample of N atoms passing sequentially through the cavity. Numerical simulations performed for the numerical values of the typical parameters setting show the effectiveness of the proposed method.

Bistability and stochastic resonance in an open quantum system

We give a detailed analysis of bistability and the associated time scales in a fundamental, driven, open quantum system, the micromaser. Under certain conditions, the quantized, nonclassical photon field in the maser cavity exhibits quantum jumps between two metastable states. We show how to calculate the corresponding transition rates, examine the influence of an injected atomic coherence, and discuss different measurement schemes to detect the final state of the exiting atoms. With these results, noise-induced effects such as stochastic resonance or suppression of higher harmonics can be understood.

Quantum integrability and quantum chaos in the micromaser

The time-dependent quantum Hamiltonians $$\hat H\left( t \right) = \left\{ {\begin{array}{*{20}c} {\hat H,t_i< t< t_i + t_{int} } \\ {\omega _0 \hat N,t_i + t_{int}< t< t_i + 1,} \\ \end{array} } \right.$$ describe a maser with N two-level atoms coupled to a single mode of a quantized field inside the maser cavity: here, ti, i=1,2,…,Na, are discrete times, Na is large (∼105), $$\hat N$$ is the number operator in the Heisenberg-Weyl (HW) algebra, and ω0 is the cavity mode frequency. The N atoms form an (N+1)-dimensional representation of the su(2) Lie algebra, the single mode forming a representation of the HW algebra. We suppose that N atoms in the excited state enter the cavity at each ti and leave at ti+t int . With all damping and finite-temperature effects neglected, this model for N=1 describes the one-atom micromaser currently in operation with85Rb atoms making microwave transitions between two high Rydberg states. We show that $$\hat H$$ is completely integrable in the quantum sense for any N-1,2,… and derive a second-order nonlinear ordinary differential equation (ODE) that determines the evolution of the inversion operator SZ(t) in the su(2) Lie algebra. For N=1 and under the nonlinear condition $$\left[ {S^Z \left( t \right)} \right]^2 = \left( {1/} \right)4\hat I$$ , this ODE linearizes to the operator form of the harmonic oscillator equation, which we solve. For N=1, the motion in the extended Hilbert space H can be a limit-cycle motion combining the motion of the atom under this nonlinear condition with the tending of the photon number n to n0 determined by $$\sqrt {n_0 + 1} gt_{int} = r\pi $$ (where r is an integer and g is the atom-field coupling constant). The motion is steady for each value of ti; at each ti, the atom-field state is |e>|n0>, where |e> is the excited state of the two-level atom and $$\left. {\left. {\hat N} \right|n_0 } \right\rangle = \left. {\left. {n_0 } \right|n_0 } \right\rangle $$ . Using a suitable loop algebra, we derive a Lax pair formulation of the operator equations of motion during the times t int for any N. For N=2 and N=3, the nonlinear operator equations linearize under appropriate additional nonlinear conditions; we obtain operator solutions for N=2 and N=3. We then give the N=2 masing solution. Having investigated the semiclassical limits of the nonlinear operator equations of motion, we conclude that “quantum chaos’ cannot be created in an N-atom micromaser for any value of N. One difficulty is the proper form of the semiclassical limits for the N-atom operator problems. Because these c-number semiclassical forms have an unstable singular point, “quantum chaos” might be created by driving the real quantum system with an additional external microwave field coupled to the maser cavity.

Trapping States in the Micromaser

Trapping states in the one-atom maser or micromaser are predicted by maser theory and are a direct consequence of the quantization of the electromagnetic field. They have been found in our experiment when the inversion of atoms leaving the cavity is observed while the interaction time is scanned. They correspond to quantum states of the atom-cavity system and under certain conditions represent Fock states. The trapping states occur when the atom-field dynamics complete a full evolution (or multiples thereof). Owing to feedback through the maser dynamics, a stabilization of the photon number in the steady state field of the maser cavity is achieved.

From Maser to Mazer

In this paper we report on atomic interferometry in the micromaser. The experimentally observed interferences are due to the non-adiabatic mixing of dressed states of the atoms at the entrance and exit holes of the maser cavity, leading to Ramsey-type two-field interaction. The observations are explained on the basis of the micromaser theory. Statistical properties of the maser field are investigated via a measurement of the statistics of the pump atoms that leave the maser cavity. Theoretical expressions for the time dependence of the Fano-Mandel-parameter QA(t) are compared with the experimental data. We demonstrate, that metastability of the maser field and atomic interference strongly influence the approach to a steady state value of QA(t). Furthermore, a theoretical investigation of a maser pumped with ultra-cold atoms is discussed. The interplay between reflection and transmission events of the atoms leads to a photon emission probability that strongly depends on the quantized center-of-mass motion (z-motion) of the atoms. We demonstrate that this mazer operation can be completely different from the ordinary maser pumped by a beam of thermal atoms.

Sonoluminescence: The effect of magnetic fields in the Planck theory

Sonoluminescence (SL) observed in the cavitation of water may be explained by the Planck theory of SL that treats the bubbles as collapsing miniature masers having a Planck energy intrinsic to the dimensions of the maser cavity. Microwaves at frequencies proportional to the collapse velocity are created in the bubble wall molecules as the Planck energy at optical frequencies is absorbed. Because of the interaction between the microwaves and molecular dipole moments, the Planck energy accumulates in the electronic state of polar molecules with a rotation quantum state. As the bubble wall is polarized, intense electrical fields develop to charge the bubble surface molecules to visible photon levels. By this theory, SL can only be observed if the maser walls close to optical dimensions thereby allowing the bubble wall molecules to accumulate Planck energy to the 3–6-eV levels necessary to produce VIS-UV photons. Closure to optical dimensions is assured by imposing a net positive collision pressure. The consistency of the Planck theory of SL was assessed with data on the effects of applied magnetic fields on SL. The net pressure was taken as the difference between the stagnation pressure in bringing the liquid bubble walls to rest and the pressure generated by the magnetic field in the presence of a charged bubble wall. Consistency with the Planck theory of SL is found as the SL intensity with magnetic field is parabolic and the peak SL intensity is linear with collapse velocity.

Entanglement and superposition states in the micromaser

In this paper recent experiments with the one–atom maser or micromaser are reviewed. They deal with the dynamical behavior of the field at parameter values where the field undergoes phase transitions. Furthermore, atomic interferences are observed in the micromaser when the inversion of the atoms leaving the cavity is measured while the cavity frequency is scanned across the atomic resonance. The interferences are due to the non–adiabatic mixing of dressed states at the entrance and exit holes of the maser cavity. The interference structures are triangular shaped and approximately equidistant. They are associated with the dynamics of the atom–field interaction, show quantum jumps and demonstrate bistability of the micromaser field.

Atomic interference in the micromaser and statistical properties of the micromaser field

In this paper we report on atomic interferometry in the micromaser. The atomic inversion is recorded while scanning the cavity frequency across the atomic resonance. For high pump rates, interference patterns are observed on the low-frequency wing of the maser line. The interferences are due to the non-adiabatic mixing of dressed states of the atoms at the entrance and exit holes of the maser cavity, leading to a Ramsey-type two-field interaction. Furthermore, statistical properties of the maser field are investigated via a measurement of the statistics of the pump atoms that leave the maser cavity. Theoretical expressions for the time dependence of the Fano–Mandel parameter Q A(t) are compared with the experimental data. We demonstrate, that metastability of the maser field and atomic interference strongly influence the approach to a steady-state value of Q A(t).

Squeezing in the Thermal Jaynes-Cummings Model

We have studied the influence of thermal photons on the symmetry between the field and atomic squeezing (SFAS) exposed in the resonant vacuum-field Jaynes-Cummings model with an initially coherent atom. We have shown that when the number of thermal photons (Nav) is less than 0.01, the SFAS is not sensitive to the presence of thermal photons; when Nav ⩾ 0.01, the broken SFAS can be seen; when Nav ⩾ 0.1, the squeezed atom cannot radiate a squeezed field any longer. Also, we have discussed the possibility of detection of the boken symmetry in superconducting maser cavity.

Atomic interferometry with the micromaser.

Atomic interferences are observed in the micromaser when the inversion of the atoms leaving the cavity is measured while the cavity frequency is scanned across the atomic resonance. The interferences are due to the nonadiabatic mixing of dressed states at the entrance and exit holes of the maser cavity. The interference structures are triangular shaped and approximately equidistant. They are associated with the dynamics of the atom-field interaction, show quantum jumps, and demonstrate bistability of the micromaser field.

The One-Atom Maser and the Generation of Nonclassical Light

We review our recent work on the nonclassical radiation field of a one-atom maser. The maser cavity is cooled to 0.5 K to exclude thermal photons and has a quality factor of 3 × 1010. Velocity-selected Rydberg atoms pump the maser. The field inside the cavity is measured via the fluctuations in the number of atoms leaving the cavity in the lower maser level which are up to 40% below the Poisson level. This corresponds to photon-number fluctuations 70% below the vacuum-state limit. The one-atom maser is the only maser system which leads to nonclassical radiation even when pumping processes with Poissonian statistics are used. We analyse and propose new experiments based on the one-atom maser leading to new studies of the quantum measurement process.

Observation of sub-Poissonian photon statistics in a micromaser.

We describe the first investigation of the nonclassical radiation field of a micromaser. The maser cavity is cooled to 0.5 K to exclude thermal photons and has a quality factor 3\ifmmode\times\else\texttimes\fi{}${10}^{10}$. Velocity-selected Rydberg atoms pump the maser. The photon statistics in the cavity are measured via the statistics of the atoms leaving the cavity in the lower maser level. Taking into account a detection efficiency of 10%, their fluctuations are reduced up to 40% below the Poisson level. This corresponds to photon-number fluctuations in the cavity of up to 70% below the vacuum-state limit.

New x-ray source for lithography

We propose the use of electromagnetic waves as an undulator in order to generate x rays in the wavelength range required for fabrication of integrated circuits. The configuration consists of a quasi-optical maser cavity through which a beam of relativistic electrons is made to propagate, spontaneously emitting x rays of the desired energy. The scaling of the x-ray power with wavelength indicates that the throughput can be increased by using resists which are sensitive to shorter wavelength x rays.

A recirculating cryogenic hydrogen maser

This paper reports on the design, theory, and initial testing of a new cryogenic hydrogen maser in which hydrogen (H) atoms circulated back and forth between a microwave-pumped state-selecting source and a small split-ring maser cavity. Initial tests observed no measurable fluctuations in the maser frequency at the level of 6 × 10−13 for measuring times between τ = 1 s and 300 s.

Application of Atomic Hydrogen at Low Temperatures: The Recirculating Cryogenic Hydrogen Maser

Conventional hydrogen masers are the most stable of all atomic clocks with stabilities Δf/f of better than 10-15 for measuring times τ of 103 sec. A new generation of cryogenic hydrogen masers has the potential to improve this figure by 2 to 3 orders of magnitude. Here we describe how research on spin-polarized atomic hydrogen led to the construction at the University of British Columbia of a uniquely cryogenic hydrogen maser. In this maser, which operates at 0.5K and uses liquid helium coated walls throughout, H atoms circulate back and forth between a microwave pumped state selector and the maser cavity. The measurement of the frequency stability is presently limited by the frequency stability of the available references, but values of Δf/f<10-13 for τ=1 sec have been recently established. The successful development of rather different cryogenic masers at other institutions will also be discussed.

Quantum theory of the micromaser: Symmetry breaking via off-diagonal atomic injection.

We propose and analyze an experiment in which atoms in a coherent superposition of atomic states are injected into a high-Q maser cavity. We show that the symmetry of the field in the cavity is ``broken'' in the same way as results from a classical signal injected into a laser cavity. This broken symmetry can be detected by monitoring the atomic excitation of a probe atom.

Recirculating cryogenic hydrogen maser

We report on the design and initial testing of a new type of hydrogen maser, operated at dilution refrigerator temperatures, in which H atoms circulate back and forth between a microwave-pumped state selector and the maser cavity. Other novel design features include liquid-/sup 4/He-coated walls, He-cooled electronics, and the use of microscopic magnetic particles to relax the two lowest hyperfine levels in the state selector. Stabilities at least as good as that of a Rb clock and a high-stability quartz oscillator are observed for measuring times between 1 and 300 s.