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Currently doing a PhD in Controlled Quantum Dynamics at Imperial College and the University of Oxford.


Jul
20
comment Introductory derivations of Heisenberg uncertainty principle
@JohnnyMo1 OK, but the current version looks fine to me, although lacking in detail. The point is that the presumption of a pre-existing value of position is in violation of the Kochen-Specker contextuality theorem; thus it is in disagreement with experiment and with quantum theory in particular. Furthermore, Heisenberg's microscope cannot account for the uncertainty arising from joint measurements on correlated quantum particles.
Jul
20
comment Introductory derivations of Heisenberg uncertainty principle
Looks like you are referring to Heisenberg's microscope. The argument is flawed for many reasons, some of which are described on the Wiki page. I'll leave it to others to give a complete answer.
Jul
18
comment In what sense is a quantum field an infinite set of harmonic oscillators?
@ACuriousMind Not true, it is perfectly possible, although unfashionable, to quantise in terms of the electric and magnetic fields. This approach is quite common in quantum optics, where preservation of Lorentz invariance is unnecessary. My point was simply that the concept of a quantum field is much more general than what one encounters in particle physics.
Jul
18
comment In what sense is a quantum field an infinite set of harmonic oscillators?
@ACuriousMind The electric field is a quantum field, which moreover is formally analogous to an infinite collection of harmonic oscillators (in the absence of sources). Are you saying that the free electric field is unobservable?
Jul
2
awarded  Curious
Jun
24
revised What do we mean when we say Bose condensation? And why can't fermions condense if they don't pair?
deleted 163 characters in body
Jun
23
comment Anyons: Effect of braiding on fusion multiplicities
Braiding and Dehn twists are both unitary operations on the fusion space. So I don't think they could change the dimension.
Jun
22
answered Density matrix formalism
Jun
20
awarded  Good Answer
Jun
20
reviewed Approve suggested edit on What do we mean when we say Bose condensation? And why can't fermions condense if they don't pair?
Jun
19
awarded  Enlightened
Jun
19
awarded  Nice Answer
Jun
19
revised What do we mean when we say Bose condensation? And why can't fermions condense if they don't pair?
added 72 characters in body
Jun
19
comment Completing the trace in the Non-abelian Chern-Simons Term
It's been a while since I did this calculation but I expect you can use the anti-symmetry of the Levi-Civita symbol $\epsilon^{\mu\nu\rho}$ to show that the unwanted symmetric combination of the gauge fields vanishes.
Jun
19
revised Why do we need high energy to explore small dimensions?
added 168 characters in body
Jun
19
answered What do we mean when we say Bose condensation? And why can't fermions condense if they don't pair?
Jun
19
answered Why do we need high energy to explore small dimensions?
Jun
17
comment Normalization of photon wavefunction and beam splitters
But the transformation $a \to \frac{a-b}{\sqrt{2}}$, $b\to \frac{a+b}{\sqrt{2}}$ is obviously unitary (in fact orthogonal).
Jun
17
comment Normalization of photon wavefunction and beam splitters
Your beam splitter transformation is not correct. An ideal beam splitter obviously implements a unitary (and thus norm-conserving) operation since the output intensity is the same as the input intensity. The beam splitter Hamiltonian looks like (schematically) $ab^{\dagger} + ba^{\dagger}$, if you exponentiate this with the right prefactor you will get the desired transformation.
Jun
7
comment University of Delft results regarding quantum teleportation of information
@jean The point of quantum teleportation is to send an (unknown) quantum state. In fact, two (classical) bits need to be sent in order to teleport the quantum state of a single qubit. Although you are correct that the physical information carrier can be interpreted as having some information content even for the eavesdropper, there is no way for them to actually reconstruct the quantum state.