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BEGIN:VEVENT
DTSTAMP:20260813T183240Z
LAST-MODIFIED:20191209T140240Z
DTSTART:20191209T160000Z
DTEND:20191209T170000Z
UID:event2252@bu.edu
URL:http://physics.bu.edu/internal/events/show/2252
SUMMARY:Finite-Size Scaling in Quantum Annealing with Decoherence
DESCRIPTION:Featuring Phillip Weinberg\n\nPart of the PhD Final Oral Exams.
	\n\nExamining Committee:  Anders Sandvik\, Anatoli Polkovnikov\, Shyam Erra
	milli\, Alex Sushkov\, David Campbell\n\nAbstract:\n\nQuantum annealing rep
	resents an essential milestone towards the goal of universal quantum comput
	ing. While quantum annealing likely may not be as powerful as universal qua
	ntum computing\, it may be better than classical algorithms. One important 
	quantity that is useful for predicting the scaling of a quantum annealing c
	alculation is the scaling of the minimum gap with problem size or the dynam
	ic exponent. We show how one can use imaginary time dynamics combined with 
	finite-size scaling to extract the dynamic exponent. Since one can calculat
	e imaginary time evolution using methods like quantum Monte Carlo or matrix
	- and tensor-product states\, one can calculate the dynamic exponent accura
	tely. \n\nIn physical realizations of quantum annealing\, there are still q
	uestions as to the role of quantum fluctuations in the operation of a devic
	e given the short coherence times of the individual qubits. These questions
	 have consistently posed a challenge to theoretical physics\, making it cha
	llenging to interpret experiments. We propose using dynamic finite-size sca
	ling to understand the nature of the fluctuations in a device. By performin
	g a systematic study comparing simulated classical and quantum annealing of
	 the 2D Ising model\, we find a difference in the scaling exponents between
	 the two types of fluctuations. We then study the behavior when performing 
	quantum annealing with decoherence observed in a physical device as a small
	 amount of noise in the transverse-field of each qubit. We compare the mode
	l to a system of manufactured qubits produced by D-wave Systems. We extend 
	the dynamic finite-size scaling to capture the competition between quantum 
	fluctuations of the transverse-field and bit-flip errors from the noise. We
	 argue that the weak noise model is more consistent with the device. These 
	results imply that at the very least\, the diagonal probabilities in the de
	nsity matrix of the system are more robust against noise compared to an iso
	lated qubit. Using this finite-size scaling\, one can diagnose sources of n
	oise in the system. Hopefully\, in the near future\, these devices will not
	 only be realizing coherent quantum annealing but will likely be useful as 
	another example of synthetic quantum matter.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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