In this study, we investigate the potential of electronic interferometers for probing the quantum state of electromagnetic radiation on a chip at subnanosecond timescales. We propose to use single-electron excitations propagating within an electronic Mach-Zehnder interferometer in the Aharonov-Bohm-dominated regime. We discuss how information about the quantum state of the electromagnetic radiation is encoded into the interference contribution to the average outgoing electrical current. By investigating squeezed radiation and single-edge magnetoplasmons probed by leviton pulses in a realistic setup, we show that single-electron interferometers have the potential to probe quantum radiation in the time domain with subnanosecond to picosecond time resolution. Our research could have significant implications for probing the fundamental properties of light in the microwave to terahertz domains at extremely short timescales.
In this study, we investigate the potential of electronic interferometers for probing the quantum state of electromagnetic radiation on a chip at subnanosecond timescales. We propose to use single-electron excitations propagating within an electronic Mach-Zehnder interferometer in the Aharonov-Bohm-dominated regime. We discuss how information about the quantum state of the electromagnetic radiation is encoded into the interference contribution to the average outgoing electrical current. By investigating squeezed radiation and single-edge magnetoplasmons probed by leviton pulses in a realistic setup, we show that single-electron interferometers have the potential to probe quantum radiation in the time domain with subnanosecond to picosecond time resolution. Our research could have significant implications for probing the fundamental properties of light in the microwave to terahertz domains at extremely short timescales.
Recent advances in quantum nano-electronics have lead to the manufacturing of electrical circuits in which quantum electrical currents involving one to a few electrons can be generated controlled and characterized. This breakthrough has spurred the development of sophisticated quantum sensing technologies, such as the electron quantum radar (EQR) introduced in this work. The EQR is an interferometric sensor leveraging both the sensitivity to electromagnetic fields and the long coherence time of single electrons to probe the quantum state of microwave radiations with subnanosecond time resolution. It is designed as a Mach-Zehnder interferometer (MZI) with one branch coupled to the radiation to be probed. As a single-electron propagates along both branches of the MZI, its wave function is altered by the radiation. This shift is imprinted in the interferences contribution to the average electrical current exiting the interferometer which then provides information about the radiation. Part of this work focuses on the shaping of single electron wave-packets and on the design of the radiation coupler which coupled the incoming single electron to the electromagnetic radiation to be probed. These two elements determine the EQR's resolving power for each probed radiation. Finally, the EQR's sensing capabilities are evaluated through specific examples, such as probing squeezed states or single photon detection, demonstrating its potential to measure properties of quantum radiation in both time and frequency domains in realistic forth coming experiments.
Characterizing quantum states of the electromagnetic field at microwave frequencies requires fast and sensitive detectors that can simultaneously probe the field's time-dependent amplitude and its quantum fluctuations. So far, this has been achieved by using either homodyne detection or fast digitizers. Both methods rely on the extraction of microwave radiation through an amplification chain towards the detector placed at room temperature, thereby limiting the time resolution to the ~10-GHz bandwidth of the measurement chain. Additionally, the coupling of high-impedance samples to the 50-Ω measurement chain is very weak, setting strong limitations on the detection sensitivity. In this work, we demonstrate an on-chip quantum sensor that exploits the phase of a single-electron wavefunction, measured in an electronic Fabry-Pérot interferometer, to detect the amplitude of a classical time-dependent electric field. The interferometer is implemented in a GaAs/AlGaAs quantum Hall conductor. The time resolution, limited by the temporal width of the electronic wavepacket, is ~35 ps. The interferometry technique provides a voltage resolution of ~50 μV, corresponding to a few microwave photons. Importantly, our detector measures both phase and contrast of the interference pattern. The latter opens the way to the detection of non-classical electromagnetic fields, such as squeezed or Fock states.
Electronic flying qubits offer an interesting alternative to photonic qubits: electrons propagate slower, hence easier to control in real time, and Coulomb interaction enables direct entanglement between different qubits. Although their coherence time is limited, flying electrons in the form of picosecond plasmonic pulses could be competitive in terms of the number of achievable coherent operations. The key challenge in achieving this critical milestone is the development of a new technology capable of injecting ‘on-demand’ single-electron wavepackets into quantum devices, with temporal durations comparable to or shorter than the device dimensions. Here, we take a significant step towards achieving this regime in a quantum nanoelectronic system by injecting ultrashort single-electron plasmonic pulses into a 14-micrometer-long Mach-Zehnder interferometer. Our results establish that quantum coherence is robust under the on-demand injection of ultrashort plasmonic pulses, as evidenced by the observation of coherent oscillations in the single-electron regime. Building on this, our results demonstrate the existence of a “non-adiabatic" regime that is prominent at high frequencies. This result highlights the potential of flying qubits as a promising alternative to localised qubit architectures, offering advantages such as a reduced hardware footprint, enhanced connectivity, and scalability for quantum information processing. The development of electronic flying qubits requires the ability to generate and control single-electron excitations. Here the authors demonstrate quantum coherence of ultrashort single-electron plasmonic pulses in an electronic Mach-Zehnder interferometer, revealing a non-adiabatic regime at high frequencies.
Electronic interferometers have been identified as possible candidates for building electronic flying qubits. Such a regime requires ultrafast voltage pulses whose duration is shorter than the time of flight through the device. Understanding the corresponding physics in the presence of such short excitations requires a proper treatment of electron-electron interactions. In this article, we take a step in this direction by performing time-resolved simulations of a Mach-Zehnder interferometer treating the interactions at the time-dependent mean-field level. We find that the main effect of the interaction is the renormalization of the pulse velocity. Very importantly, the interference effects appear to be robust to the presence of interactions.
Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of V T H z ∼ 10 − 9 ( λ T H z / 2 ) 3 in combination with ultraperformant organic molecules ( r 33 = 170 p m / V ) and accomplish a record-high single-photon electro-optic coupling rate of g e o = 2 π × 0.043 G H z , 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is C 0 = 1.6 × 10 − 8 , and the multiphoton cooperativity is C = 0.002 at room temperature. We show > 70 d B dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.
Abstract The development of single‐electron sources is paving the way for a novel type of experiment in which individual electrons are emitted into a quantum‐coherent circuit. However, to facilitate further progress toward fully coherent on‐chip experiments with electrons, a detailed understanding of the quantum circuits is needed. Here, it is proposed to perform time‐domain spectroscopy of mesoscopic conductors by applying Lorentzian‐shaped voltage pulses to an input contact. Specifically, it is shown how characteristic timescales of a quantum‐coherent conductor can be extracted from the distribution of waiting times between charge pulses propagating through the circuit. To illustrate the idea, Floquet scattering theory is employed to evaluate the electron waiting times for an electronic Fabry–Pérot cavity and a Mach–Zehnder interferometer. The perspectives for an experimental realization of the proposal are discussed and possible avenues for further developments are identified.