16 research outputs found
Contactless photoconductivity-detected electron spin resonance of P donors in isotopically purified Si
Coherence times of electron spins bound to phosphorus donors have been
measured, using a standard Hahn echo technique, to be up to 20 ms in
isotopically pure silicon with [P] cm and at temperatures
K. Although such times are exceptionally long for electron spins in
the solid state, they are nevertheless limited by donor electron spin-spin
interactions. Suppressing such interactions requires even lower donor
concentrations, which lie below the detection limit for typical electron spin
resonance (ESR) spectrometers. Here we describe an alternative method for
phosphorus donor ESR detection, exploiting the spin-to-charge conversion
provided by the optical donor bound exciton transition. We characterise the
method and its dependence on laser power and use it to measure a coherence time
of ms for one of the purest silicon samples grown to-date ([P]cm). We then benchmark this result using an alternative
application of the donor bound exciton transition: optically polarising the
donor spins before using conventional ESR detection at 1.7~K for a sample with
[P]cm, and measuring in this case a of 350 ms
Violation of a Leggett-Garg inequality with ideal non-invasive measurements
The quantum superposition principle states that an entity can exist in two
different states simultaneously, counter to our 'classical' intuition. Is it
possible to understand a given system's behaviour without such a concept? A
test designed by Leggett and Garg can rule out this possibility. The test,
originally intended for macroscopic objects, has been implemented in various
systems. However to-date no experiment has employed the 'ideal negative result'
measurements that are required for the most robust test. Here we introduce a
general protocol for these special measurements using an ancillary system which
acts as a local measuring device but which need not be perfectly prepared. We
report an experimental realisation using spin-bearing phosphorus impurities in
silicon. The results demonstrate the necessity of a non-classical picture for
this class of microscopic system. Our procedure can be applied to systems of
any size, whether individually controlled or in a spatial ensemble.Comment: 6+4 pages. Supplementary Methods section include
Room temperature quantum bit storage exceeding 39 minutes using ionized donors in 28-silicon
Quantum memories capable of storing and retrieving coherent information for
extended times at room temperature would enable a host of new technologies.
Electron and nuclear spin qubits using shallow neutral donors in semiconductors
have been studied extensively but are limited to low temperatures (10 K);
however, the nuclear spins of ionized donors have potential for high
temperature operation. We use optical methods and dynamical decoupling to
realize this potential for an ensemble of 31P donors in isotopically purified
28Si and observe a room temperature coherence time of over 39 minutes. We
further show that a coherent spin superposition can be cycled from 4.2 K to
room temperature and back, and report a cryogenic coherence time of 3 hours in
the same system.Comment: 5 pages, 4 figure
Geometric Phase Gates with Adiabatic Control in Electron Spin Resonance
High-fidelity quantum operations are a key requirement for fault-tolerant
quantum information processing. In electron spin resonance, manipulation of the
quantum spin is usually achieved with time-dependent microwave fields. In
contrast to the conventional dynamic approach, adiabatic geometric phase
operations are expected to be less sensitive to certain kinds of noise and
field inhomogeneities. Here, we investigate such phase gates applied to
electron spins both through simulations and experiments, showing that the
adiabatic geometric phase gate is indeed inherently robust against
inhomogeneity in the applied microwave field strength. While only little
advantage is offered over error-correcting composite pulses for modest
inhomogeneities <=10%, the adiabatic approach reveals its potential for
situations where field inhomogeneities are unavoidably large