The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold.

We study a voltage biased InAs double quantum dot (DQD) that is coupled to a superconducting transmission line resonator. Inelastic tunneling in the DQD is mediated by electron phonon coupling and coupling to the cavity mode. We show that electronic transport through the DQD leads to photon emission from the cavity at a rate of 10 MHz. With a small cavity drive field, we observe a gain of up to 15 in the cavity transmission. Our results are analyzed in the context of existing theoretical models and suggest that it may be necessary to account for inelastic tunneling processes that proceed via simultaneous emission of a phonon and a photon.

We report the observation of multiple harmonic generation in electric dipole spin resonance in an InAs nanowire double quantum dot. The harmonics display a remarkable detuning dependence: near the interdot charge transition as many as eight harmonics are observed, while at large detunings we only observe the fundamental spin resonance condition. The detuning dependence indicates that the observed harmonics may be due to Landau-Zener transition dynamics at anticrossings in the energy level spectrum.

We perform Landau-Zener-Stückelberg interferometry on a single electron GaAs charge qubit by repeatedly driving the system through an avoided crossing. We observe coherent destruction of tunneling, where periodic driving with specific amplitudes inhibits current flow. We probe the quantum dot occupation using a charge detector, observing oscillations in the qubit population resulting from the microwave driving. At a frequency of 9 GHz we observe excitation processes driven by the absorption of up to 17 photons. Simulations of the qubit occupancy are in good agreement with the experimental data.PACS numbers: 73.21. La, 73.63.Kv, 85.35.Be, 85.35.Ds Semiconductor quantum dots are fruitful systems for exploring phenomena arising from quantum interference effects [1][2][3][4][5][6]. Landau-Zener-Stückelberg (LZS) interferometry has recently emerged as a novel way to study quantum coherence in solid state systems. LZS theory was initially described in the context of atomic collisions and relies on having an effective two-level system with an avoided crossing in the energy level spectrum [7][8][9][10][11]. Repeated sweeps through the avoided crossing result in successive Landau-Zener transitions, allowing control of the final state probability. While the theory was initially applied to atomic collisions, recent advances in the fabrication of solid state quantum devices have made it experimentally accessible in a wide variety of systems, ranging from superconducting qubits [12] to nitrogen vacancy centers in diamond [13,14]. In superconducting qubits, LZS interferometry has been used with great success to determine the energy level diagram and to measure qubit coherence times [12,15,16]. In spin qubits, LZS interferometry has been harnessed to drive coherent singlet-triplet transitions resulting in spin rotations that are much faster than those obtained using conventional electron spin resonance [17,18].In this Rapid Communication we perform LZS interferometry on a single electron GaAs double quantum dot (DQD) charge qubit. The sample geometry is illustrated in the scanning electron microscope (SEM) image shown in Fig. 1(a). Ti/Au gate electrodes are fabricated on top of a GaAs/AlGaAs heterostructure that is grown using molecular beam epitaxy. The gate electrodes selectively deplete regions of the two-dimensional electron gas located 110 nm below the surface of the wafer, forming a DQD containing a single electron. In this experiment, a third dot is used as a charge detector, which allows non-invasive measurements of the charge state occupancy [19]. A fixed 100 mT field is applied perpendicular to the plane of the sample. Despite their simplicity, charge qubits are of great experimental importance as they allow for direct quantum control through electric fields, with coherent control rates dictated by tunnel couplings that can easily approach 10 GHz. They also serve as building blocks for more complex quantum systems, such as spin qubits [20].We focus on the one electron regime, where the DQD contains a single charge...

We demonstrate fast readout of a double quantum dot (DQD) that is coupled to a superconducting resonator. Utilizing parametric amplification in a nonlinear operational mode, we improve the signalto-noise ratio (SNR) by a factor of 2000 compared to the situation with the parametric amplifier turned off. With an integration time of 400 ns we achieve a SNR of 76. By studying SNR as a function of the integration time we extract an equivalent charge sensitivity of 8 × 10 −5 e/ √ Hz. The high SNR allows us to acquire a DQD charge stability diagram in just 20 ms. At such a high data rate, it is possible to acquire charge stability diagrams in a live "video-mode," enabling real time tuning of the DQD confinement potential.