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BEGIN:VEVENT
DTSTAMP:20261014T190329Z
LAST-MODIFIED:20201203T214209Z
DTSTART:20201211T153000Z
DTEND:20201211T163000Z
UID:event2386@bu.edu
URL:http://physics.bu.edu/internal/events/show/2386
SUMMARY:Experimental Realization of Spin Liquids in a Programmable Quantum 
	Device
DESCRIPTION:Featuring Shiyu Zhou\, Boston University\, Physics Department\n
	\nPart of the Preliminary Oral Exam.\n\nQuantum spin liquids (QSL) have a l
	ong history. They were first proposed in the 1970s by Anderson [1] as an al
	ternative to the spin 1/2 N´eel antiferromagnetic state\, and later as can
	didates for the insulating parent state of the high-temperature superconduc
	tors[2]. QSLs are closely related to lattice gauge models in particle physi
	cs\, also dating to the 1970s [3–5]. Today\, a QSL model known as the tor
	ic code is a potential platform for topological computing [6]. There have b
	een many proposed materials\, but to-date gapped QSLs have not been unambig
	uously observed in nature [7]. Since they are so hard to find in materials\
	, a more recent idea is to build a QSL synthetically out of superconducting
	 circuits [8–10]. In this talk I will take these ideas one step further a
	nd show that\, in principle\, a programmable device can be used to emulate 
	QSL phases so far unreachable by other means\, a step towards realizing log
	ical topological qubits in these same devices. We build and probe a Z2 spin
	 liquid in a programmable quantum device\, the D-Wave DW-2000Q. To realize 
	this state of matter\, we design a Hamiltonian with combinatorial gauge sym
	metry [11] using only pairwise-qubit interactions and a transverse field\, 
	i.e.\, interactions which are accessible in this quantum device. The combin
	atorial gauge symmetry remains exact along the full quantum annealing path\
	, landing the system onto the classical 8-vertex model at the endpoint of t
	he path. The output configurations from the device allows us to directly ob
	serve the loop structure of the model. Moreover\, we deform the Hamiltonian
	 so as to vary the weights of the 8 vertices and show that we can selective
	ly attain the 6-vertex (ice model)\, or drive the system into a ferromagnet
	ic state. We present studies of the phase diagram of the system as function
	 of the 8-vertex deformations and effective temperature\, which we control 
	by varying the relative strengths of the programmable couplings\, and we sh
	ow that the experimental results are consistent with theoretical analysis. 
	Finally\, we identify additional capabilities that\, if added to these quan
	tum devices\, would allow us to realize Z2 quantum spin liquids on which to
	 build topological qubits.\n \n\n[1] P. Anderson\, "Resonating valence bond
	s: A new kind of insulator?" Materials Research Bulletin 8\, 153 – 160 (1
	973).\n\n[2] P. W. Anderson\, "The resonating valence bond state in La2CuO4
	 and superconductivity\," Science 235\, 1196–1198 (1987). \n\n[3] F. J. W
	egner\, "Duality in generalized Ising models and phase transitions without 
	local order parameters\," J. Math. Phys. 12\, 2259–2272 (1971).\n\n[4] J.
	 B. Kogut\, "An introduction to lattice gauge theory and spin systems\," Re
	v. Mod. Phys. 51\, 659–713 (1979).\n\n[5] E. Fradkin and L. Susskind\, "O
	rder and disorder in gauge systems and magnets\," Phys. Rev. D 17\, 2637–
	2658 (1978).\n\n[6] A. Y. Kitaev\, "Fault-tolerant quantum computation by a
	nyons\," Ann. Phys. 303\, 2–30 (2003).\n\n[7] L. Savary and L. Balents\, 
	"Quantum spin liquids: a review\," Reports on Progress in Physics 80\, 0165
	02 (2016).\n\n[8] L. B. Ioffe\, M. V. Feigel’man\, A. Ioselevich\, D. Iva
	nov\, M. Troyer\, and G. Blatter\, "Topologically protected quantum bits us
	ing Josephson junction arrays\," Nature 415\, 503–506 (2002).\n\n[9] L. B
	. Ioffe and M. V. Feigel’man\, "Possible realization of an ideal quantum 
	computer in Josephson junction array\," Phys. Rev. B 66\, 224503 (2002).\n\
	n[10] C. Chamon and D. Green\, "A superconducting circuit realization of co
	mbinatorial gauge symmetry\," (2020)\, arXiv:2006.10060.\n\n[11] C. Chamon\
	, D. Green\, and Z.-C. Yang\, "Constructing quantum spin liquids using comb
	inatorial gauge symmetry\," Phys. Rev. Lett. 125\, 067203 (2020).\n\n\n----
	\nTime: Dec 11\, 2020 10:30 AM Eastern Time (US and Canada)\n\nJoin Zoom Me
	eting\nhttps://bostonu.zoom.us/j/91756070591?pwd=cjlYaDdHc2daOERCOThIWVhDcn
	B3Zz09
LOCATION: \, \, 
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