16 research outputs found
A photonic quantum information interface
Quantum communication is the art of transferring quantum states, or quantum
bits of information (qubits), from one place to another. On the fundamental
side, this allows one to distribute entanglement and demonstrate quantum
nonlocality over significant distances. On the more applied side, quantum
cryptography offers, for the first time in human history, a provably secure way
to establish a confidential key between distant partners. Photons represent the
natural flying qubit carriers for quantum communication, and the presence of
telecom optical fibres makes the wavelengths of 1310 and 1550 nm particulary
suitable for distribution over long distances. However, to store and process
quantum information, qubits could be encoded into alkaline atoms that absorb
and emit at around 800 nm wavelength. Hence, future quantum information
networks made of telecom channels and alkaline memories will demand interfaces
able to achieve qubit transfers between these useful wavelengths while
preserving quantum coherence and entanglement. Here we report on a qubit
transfer between photons at 1310 and 710 nm via a nonlinear up-conversion
process with a success probability greater than 5%. In the event of a
successful qubit transfer, we observe strong two-photon interference between
the 710 nm photon and a third photon at 1550 nm, initially entangled with the
1310 nm photon, although they never directly interacted. The corresponding
fidelity is higher than 98%.Comment: 7 pages, 3 figure
Spectral compression of single photons
Photons are critical to quantum technologies since they can be used for
virtually all quantum information tasks: in quantum metrology, as the
information carrier in photonic quantum computation, as a mediator in hybrid
systems, and to establish long distance networks. The physical characteristics
of photons in these applications differ drastically; spectral bandwidths span
12 orders of magnitude from 50 THz for quantum-optical coherence tomography to
50 Hz for certain quantum memories. Combining these technologies requires
coherent interfaces that reversibly map centre frequencies and bandwidths of
photons to avoid excessive loss. Here we demonstrate bandwidth compression of
single photons by a factor 40 and tunability over a range 70 times that
bandwidth via sum-frequency generation with chirped laser pulses. This
constitutes a time-to-frequency interface for light capable of converting
time-bin to colour entanglement and enables ultrafast timing measurements. It
is a step toward arbitrary waveform generation for single and entangled
photons.Comment: 6 pages (4 figures) + 6 pages (3 figures
Efficient quantum computing using coherent photon conversion
Single photons provide excellent quantum information carriers, but current
schemes for preparing, processing and measuring them are inefficient. For
example, down-conversion provides heralded, but randomly timed single photons,
while linear-optics gates are inherently probabilistic. Here, we introduce a
deterministic scheme for photonic quantum information. Our single, versatile
process---coherent photon conversion---provides a full suite of photonic
quantum processing tools, from creating high-quality heralded single- and
multiphoton states free of higher-order imperfections to implementing
deterministic multiqubit entanglement gates and high-efficiency detection. It
fulfils all requirements for a scalable photonic quantum computing
architecture. Using photonic crystal fibres, we experimentally demonstrate a
four-colour nonlinear process usable for coherent photon conversion and show
that current technology provides a feasible path towards deterministic
operation. Our scheme, based on interacting bosonic fields, is not restricted
to optical systems, but could also be implemented in optomechanical,
electromechanical and superconducting systems which exhibit extremely strong
intrinsic nonlinearities.Comment: 12 pages, 9 figure
Photonic quantum technologies
The first quantum technology, which harnesses uniquely quantum mechanical
effects for its core operation, has arrived in the form of commercially
available quantum key distribution systems that achieve enhanced security by
encoding information in photons such that information gained by an eavesdropper
can be detected. Anticipated future quantum technologies include large-scale
secure networks, enhanced measurement and lithography, and quantum information
processors, promising exponentially greater computation power for particular
tasks. Photonics is destined for a central role in such technologies owing to
the need for high-speed transmission and the outstanding low-noise properties
of photons. These technologies may use single photons or quantum states of
bright laser beams, or both, and will undoubtably apply and drive
state-of-the-art developments in photonics
Engineering of microfabricated ion traps and integration of advanced on-chip features
Atomic ions trapped in electromagnetic potentials have long been used for fundamental studies in quantum physics. Over the past two decades, trapped ions have been successfully used to implement technologies such as quantum computing, quantum simulation, atomic clocks, mass spectrometers and quantum sensors. Advanced fabrication techniques, taken from other established or emerging disciplines, are used to create new, reliable ion-trap devices aimed at large-scale integration and compatibility with commercial fabrication. This Technical Review covers the fundamentals of ion trapping before discussing the design of ion traps for the aforementioned applications. We overview the current microfabrication techniques and the various considerations behind the choice of materials and processes. Finally, we discuss current efforts to include advanced, on-chip features in next-generation ion traps
Impact of ionizing radiation on superconducting qubit coherence
© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Technologies that rely on quantum bits (qubits) require long coherence times and high-fidelity operations1. Superconducting qubits are one of the leading platforms for achieving these objectives2,3. However, the coherence of superconducting qubits is affected by the breaking of Cooper pairs of electrons4–6. The experimentally observed density of the broken Cooper pairs, referred to as quasiparticles, is orders of magnitude higher than the value predicted at equilibrium by the Bardeen–Cooper–Schrieffer theory of superconductivity7–9. Previous work10–12 has shown that infrared photons considerably increase the quasiparticle density, yet even in the best-isolated systems, it remains much higher10 than expected, suggesting that another generation mechanism exists13. Here we provide evidence that ionizing radiation from environmental radioactive materials and cosmic rays contributes to this observed difference. The effect of ionizing radiation leads to an elevated quasiparticle density, which we predict would ultimately limit the coherence times of superconducting qubits of the type measured here to milliseconds. We further demonstrate that radiation shielding reduces the flux of ionizing radiation and thereby increases the energy-relaxation time. Albeit a small effect for today’s qubits, reducing or mitigating the impact of ionizing radiation will be critical for realizing fault-tolerant superconducting quantum computers