35 research outputs found
Wafer-scale nanofabrication of telecom single-photon emitters in silicon
A highly promising route to scale millions of qubits is to use quantum photonic integrated circuits (PICs), where deterministic photon sources, reconfigurable optical elements, and single-photon detectors are monolithically integrated on the same silicon chip. The isolation of single-photon emitters, such as the G centers and W centers, in the optical telecommunication O-band, has recently been realized in silicon. In all previous cases, however, single-photon emitters were created uncontrollably in random locations, preventing their scalability. Here, we report the controllable fabrication of single G and W centers in silicon wafers using focused ion beams (FIB) with high probability. We also implement a scalable, broad-beam implantation protocol compatible with the complementary-metal-oxide-semiconductor (CMOS) technology to fabricate single telecom emitters at desired positions on the nanoscale. Our findings unlock a clear and easily exploitable pathway for industrial-scale photonic quantum processors with technology nodes below 100 nm
Characterization of the Si:Se+ Spin-Photon Interface
Silicon is the most-developed electronic and photonic technological platform and hosts some of the highest-performance spin and photonic qubits developed to date. A hybrid quantum technology harnessing an efficient spin-photon interface in silicon would unlock considerable potential by enabling ultralong-lived photonic memories, distributed quantum networks, microwave-to-optical photon converters, and spin-based quantum processors, all linked with integrated silicon photonics. However, the indirect band gap of silicon makes identification of efficient spin-photon interfaces nontrivial. Here we build upon the recent identification of chalcogen donors as a promising spin-photon interface in silicon. We determine that the spin-dependent optical degree of freedom has a transition dipole moment stronger than previously thought [here 1.96(8) D], and the spin T1 lifetime in low magnetic fields is longer than previously thought [here longer than 4.6(1.5) h]. We furthermore determine the optical excited-state lifetime [7.7(4) ns], and therefore the natural radiative efficiency [0.80(9)%], and by measuring the phonon sideband determine the zero-phonon emission fraction [16(1)%]. Taken together, these parameters indicate that an integrated quantum optoelectronic platform based on chalcogen-donor qubits in silicon is well within reach of current capabilities
Electronic Properties and Structure of BoronâHydrogen Complexes in Crystalline Silicon
From Wiley via Jisc Publications RouterHistory: received 2021-06-27, rev-recd 2021-09-04, pub-electronic 2021-09-17Article version: VoRPublication status: PublishedFunder: Department of Science and Technology (DOST), Government of the PhlippinesFunder: Fundação para a CiĂȘncia e a Tecnologia in Portugal; Grant(s): UIDB/50025/2020, UIDP/50025/2020The subject of hydrogenâboron interactions in crystalline silicon is revisited with reference to light and elevated temperatureâinduced degradation (LeTID) in boronâdoped solar silicon. Ab initio modeling of structure, binding energy, and electronic properties of complexes incorporating a substitutional boron and one or two hydrogen atoms is performed. From the calculations, it is confirmed that a BH pair is electrically inert. It is found that boron can bind two H atoms. The resulting BH2 complex is a donor with a transition level estimated at E câ0.24 eV. Experimentally, the electrically active defects in nâtype Czochralskiâgrown Si crystals coâdoped with phosphorus and boron, into which hydrogen is introduced by different methods, are investigated using junction capacitance techniques. In the deepâlevel transient spectroscopy (DLTS) spectra of hydrogenated Si:P + B crystals subjected to heatâtreatments at 100 °C under reverse bias, an electron emission signal with an activation energy of â0.175 eV is detected. The trap is a donor with electronic properties close to those predicted for boronâdihydrogen. The donor character of BH2 suggests that it can be a very efficient recombination center of minority carriers in Bâdoped pâtype Si crystals. A sequence of boronâhydrogen reactions, which can be related to the LeTID effect in Si:B is proposed
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A photonic platform for donor spin qubits in silicon
Donor spins in silicon are highly competitive qubits for upcoming quantum technologies, offering complementary metal-oxide semiconductor compatibility, coherence (T2) times of minutes to hours, and simultaneous initialization, manipulation, and readout fidelities near ~99.9%. This allows for many quantum error correction protocols, which will be essential for scale-up. However, a proven method of reliably coupling spatially separated donor qubits has yet to be identified. We present a scalable silicon-based platform using the unique optical properties of âdeepâ chalcogen donors. For the prototypical 77Se+ donor, we measure lower bounds on the transition dipole moment and excited-state lifetime, enabling access to the strong coupling limit of cavity quantum electrodynamics using known silicon photonic resonator technology and integrated silicon photonics. We also report relatively strong photon emission from this same transition. These results unlock clear pathways for silicon-based quantum computing, spin-to-photon conversion, photonic memories, integrated single-photon sources, and all-optical switches
Low-frequency spin qubit energy splitting noise in highly purified 28Si/SiGe
We identify the dominant source for low-frequency spin qubit splitting noise in a highly isotopically-purified silicon device with an embedded nanomagnet and a spin echo decay time Techo2â=â128â”s. The power spectral density (PSD) of the charge noise explains both, the clear transition from a 1/f2- to a 1/f-dependence of the splitting noise PSD as well as the experimental observation of a decreasing time-ensemble spin dephasing time, from Tâ2ââ20â”s, with increasing measurement time over several hours. Despite their strong hyperfine contact interaction, the few 73Ge nuclei overlapping with the quantum dot in the barrier do not limit Tâ2, likely because their dynamics is frozen on a few hours measurement scale. We conclude that charge noise and the design of the gradient magnetic field are the key to further improve the qubit fidelity in isotopically purified 28Si/SiGe
Millisecond electron spin coherence time for erbium ions in silicon
Spins in silicon that are accessible via a telecom-compatible optical
transition are a versatile platform for quantum information processing that can
leverage the well-established silicon nanofabrication industry. Key to these
applications are long coherence times on the optical and spin transitions to
provide a robust system for interfacing photonic and spin qubits. Here, we
report telecom-compatible Er3+ sites with long optical and electron spin
coherence times, measured within a nuclear spin-free silicon crystal (<0.01%
29Si) using optical detection. We investigate two sites and find 0.1 GHz
optical inhomogeneous linewidths and homogeneous linewidths below 70 kHz for
both sites. We measure the electron spin coherence time of both sites using
optically detected magnetic resonance and observe Hahn echo decay constants of
0.8 ms and 1.2 ms at around 11 mT. These optical and spin properties of Er3+:Si
are an important milestone towards using optically accessible spins in silicon
for a broad range of quantum information processing applications.Comment: 14 pages, 6 figure
IndiumâDoped Silicon for Solar CellsâLightâInduced Degradation and DeepâLevel Traps
From Wiley via Jisc Publications RouterHistory: received 2021-02-28, rev-recd 2021-06-11, pub-electronic 2021-07-21Article version: VoRPublication status: PublishedFunder: EPSRC (UK); Grant(s): EP/TO25131/1Funder: Department of Science and Technology (DOST), Government of the PhlippinesFunder: Fundação para a CiĂȘncia e a Tecnologia; Id: http://dx.doi.org/10.13039/100008382; Grant(s): UIDB/50025/2020, UIDP/50025/2020Indiumâdoped silicon is considered a possible pâtype material for solar cells to avoid lightâinduced degradation (LID), which occurs in cells made from boronâdoped Czochralski (Cz) silicon. Herein, the defect reactions associated with indiumârelated LID are examined and a deep donor is detected, which is attributed to a negativeâU defect believed to be InsO2. In the presence of minority carriers or above bandgap light, the deep donor transforms to a shallow acceptor. An analogous transformation in boronâdoped material is related to the BsO2 defect that is a precursor of the center responsible for BO LID. The electronic properties of InsO2 are determined and compared to those of the BsO2 defect. Structures of the BsO2 and InsO2 defects in different charges states are found using firstâprinciples modeling. The results of the modeling can explain both the similarities and the differences between the BsO2 and InsO2 properties
High-fidelity operation and algorithmic initialisation of spin qubits above one kelvin
The encoding of qubits in semiconductor spin carriers has been recognised as
a promising approach to a commercial quantum computer that can be
lithographically produced and integrated at scale. However, the operation of
the large number of qubits required for advantageous quantum applications will
produce a thermal load exceeding the available cooling power of cryostats at
millikelvin temperatures. As the scale-up accelerates, it becomes imperative to
establish fault-tolerant operation above 1 kelvin, where the cooling power is
orders of magnitude higher. Here, we tune up and operate spin qubits in silicon
above 1 kelvin, with fidelities in the range required for fault-tolerant
operation at such temperatures. We design an algorithmic initialisation
protocol to prepare a pure two-qubit state even when the thermal energy is
substantially above the qubit energies, and incorporate high-fidelity
radio-frequency readout to achieve an initialisation fidelity of 99.34 per
cent. Importantly, we demonstrate a single-qubit Clifford gate fidelity of
99.85 per cent, and a two-qubit gate fidelity of 98.92 per cent. These advances
overcome the fundamental limitation that the thermal energy must be well below
the qubit energies for high-fidelity operation to be possible, surmounting a
major obstacle in the pathway to scalable and fault-tolerant quantum
computation
High-fidelity spin qubit operation and algorithmic initialization above 1 K
The encoding of qubits in semiconductor spin carriers has been recognized as a promising approach to a commercial quantum computer that can be lithographically produced and integrated at scale. However, the operation of the large number of qubits required for advantageous quantum applications will produce a thermal load exceeding the available cooling power of cryostats at millikelvin temperatures. As the scale-up accelerates, it becomes imperative to establish fault-tolerant operation above 1âK, at which the cooling power is orders of magnitude higher. Here we tune up and operate spin qubits in silicon above 1âK, with fidelities in the range required for fault-tolerant operations at these temperatures. We design an algorithmic initialization protocol to prepare a pure two-qubit state even when the thermal energy is substantially above the qubit energies and incorporate radiofrequency readout to achieve fidelities up to 99.34% for both readout and initialization. We also demonstrate single-qubit Clifford gate fidelities up to 99.85% and a two-qubit gate fidelity of 98.92%. These advances overcome the fundamental limitation that the thermal energy must be well below the qubit energies for the high-fidelity operation to be possible, surmounting a main obstacle in the pathway to scalable and fault-tolerant quantum computation