T. Ferrus

Experimental Observation of Enhanced Electron–Phonon Interaction in Suspended Si Double Quantum Dots

Silicon-based suspended double quantum dots (SDQDs) were fabricated to study and control the strength of the electron–phonon interaction. A distinctive and large inelastic tunneling was observed in single-electron transport measurement and well explained by the emission of phonons that interact strongly with electrons owing to the phonon modulation in the suspended film. The first time observation of the enhancement of the electron–phonon interaction in Si SDQDs as well as the good agreement between the experimental results and the theoretical simulations are encouraging preliminary results that allow us to envision the observation of the tailoring of the electron–phonon interaction in SDQDs.

Fine and Large Coulomb Diamonds in a Silicon Quantum Dot

We experimentally study the transport properties of silicon quantum dots (QDs) fabricated from a highly doped n-type silicon-on-insulator wafer. Low noise electrical measurements using a low temperature complementary metal-oxide-semiconductor (LTCMOS) amplifier are performed at 4.2 K in liquid helium. Two series of Coulomb peaks are observed: long-period oscillations and fine structures, and both of them show clear source drain voltage dependence. We also observe two series of Coulomb diamonds having different periodicity. The obtained experimental results are well reproduced by a master equation analysis using a model of double QDs coupled in parallel.

Electron temperature in electrically isolated Si double quantum dots

Charge-based quantum computation can be attained through reliable control of single electrons in lead-less quantum systems. Single-charge transitions in electrically isolated double quantum dots (DQDs) realised in phosphorus-doped silicon can be detected via capacitively coupled single-electron tunnelling devices. By means of time-resolved measurements of the detector’s conductance, we investigate the dots’ occupancy statistics in temperature. We observe a significant reduction of the effective electron temperature in the DQD as compared to the temperature in the detector’s leads. This sets promises to make isolated DQDs suitable platforms for long-coherence quantum computation.

Cryogenic instrumentation for fast current measurement in a silicon single electron transistor

We present a realization of high bandwidth instrumentation at cryogenic temperatures and for dilution refrigerator operation that possesses advantages over methods using radio frequency single electron transistor or transimpedance amplifiers. The ability for the low temperature electronics to carry out faster measurements than with room temperature electronics is investigated by the use of a phosphorous-doped single electron transistor. A single shot technique is successfully implemented and used to observe the real-time decay of a quantum state. A discussion on various measurement strategies is presented and the consequences on electron heating and noise are analyzed.

Charge detection in phosphorus-doped silicon double quantum dots

We report charge detection in degenerately phosphorus-doped silicon double quantum dots (DQD) electrically connected to an electron reservoir. The sensing device is a single electron transistor (SET) patterned in close proximity to the DQD. Measurements performed at 4.2K show step-like behaviour and shifts of the Coulomb Blockade oscillations in the detector’s current as the reservoir’s potential is swept. By means of a classical capacitance model, we demonstrate that the observed features can be used to detect single-electron tunnelling from, to and within the DQD, as well as to reveal the DQD charge occupancy.The ability to control and detect single electrons is paramount for the implementation of a scalable charge-based quantum computer and single-electron memory devices. Here, we report charge detection in degenerately phosphorus-doped silicon double quantum dots (DQD) that are electrically connected to an electron reservoir. The sensing device is a single-electron transistor patterned in close proximity to the DQD. We observe steplike behavior and shifts of the Coulomb blockade oscillations in the detector’s current as the reservoir’s potential is swept. By means of a classical capacitance model, we demonstrate that these features can be used to detect changes in the DQD charge occupancy.

Localization effects in the tunnel barriers of phosphorus-doped silicon quantum dots

We have observed a negative differential conductance with singular gate and source-drain bias dependences in a phosphorus-doped silicon quantum dot. Its origin is discussed within the framework of weak localization. By measuring the current-voltage characteristics at different temperatures as well as simulating the tunneling rates dependences on energy, we demonstrate that the presence of shallow energy defects together with an enhancement of localization satisfactory explain our observations. Effects observed in magnetic fields are also discussed.

Realization of Lithographically‐Defined Silicon Quantum Dots without Unintentional Localized Potentials

We have fabricated lithographically‐defined Si quantum dots (QDs) within a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) structure. In this architecture, the top gate is used to tune the carrier density whereas side gates control the potentials of the QDs and tunneling barriers. These lithographically‐defined and electrically‐tunable Si QDs were successfully realized without unintentional localized potentials.

Detection of variable tunneling rates in silicon quantum dots

Reliable detection of single electron tunneling in quantum dots (QDs) is paramount to use this category of device for quantum information processing. Here, we report charge sensing in a degenerately phosphorus-doped silicon QD by means of a capacitively coupled single-electron tunneling device made of the same material. Besides accurate counting of tunneling events in the QD, we demonstrate that this architecture can be operated to reveal asymmetries in the transport characteristic of the QD. Indeed, the observation of gate voltage shifts in the detector’s response as the QD bias is changed is an indication of variable tunneling rates.

Charge sensing of two isolated double quantum dots

We report the charge sensing of two isolated double quantum dots (IDQDs) at 4.2 K. The structure is fabricated through trench isolation of highly doped n-type silicon on silicon-on-insulator wafer. Each device contains one pair of IDQDs and one single electron transistor (SET) which serves as an electrometer. We detect the charge motion in each IDQD and the results are consistent with the simulation.

Manipulation of silicon quantum dots and isolated structures using GHz photons

We demonstrate that microwave photons can be used to remotely manipulate electron tunneling across a tunnel barrier at 4.2 K. A similar method is used to successfully modify the charges states of an electrically isolated doped silicon double quantum dot with potential coherence time of the order of a few μs.