Journal of Inequalities in Pure and Applied Mathematics ON THE SHARPENED HEISENBERG-WEYL INEQUALITY JOHN MICHAEL RASSIAS Pedagogical Department, E. E. National and Capodistrian University of Athens Section of Mathematics and Informatics 4, Agamemnonos Str., Aghia Paraskevi Athens 15342, Greece. volume 7, issue 3, article 80, 2006. Received 21 June, 2005; accepted 21 July, 2006. Communicated by: S. Saitoh EMail: jrassias@primedu.uoa.gr URL: http://www.primedu.uoa.gr/∼jrassias/ Abstract Contents JJ J II I Home Page Go Back Close c 2000 Victoria University ISSN (electronic): 1443-5756 188-05 Quit Abstract The well-known second order moment Heisenberg-Weyl inequality (or uncertainty relation) in Fourier Analysis states: Assume that f : R → C is a complex valued function of a random real variable x such that f ∈ L2 (R). Then the product of the second moment of the random real x for |f|2 and the second 2 . moment of the random real ξ for fˆ is at least E|f|2 4π, where fˆ is the Fourier R R transform of f, such that fˆ (ξ) = R e−2iπξx f (x) dx, f (x) = R e2iπξx fˆ (ξ) dξ, R and E|f|2 = R |f (x)|2 dx. This uncertainty relation is well-known in classical quantum mechanics. In 2004, the author generalized the afore-mentioned result to higher order moments and in 2005, he investigated a Heisenberg-Weyl type inequality without Fourier transforms. In this paper, a sharpened form of this generalized Heisenberg-Weyl inequality is established in Fourier analysis. Afterwards, an open problem is proposed on some pertinent extremum principle.These results are useful in investigation of quantum mechanics. On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J 2000 Mathematics Subject Classification: 26, 33, 42, 60, 52. Key words: Sharpened, Heisenberg-Weyl inequality, Gram determinant. Go Back Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Second Order Moment Heisenberg-Weyl Inequality . 1.2 Fourth Order Moment Heisenberg-Weyl Inequality . . 2 Sharpened Heisenberg-Weyl Inequality . . . . . . . . . . . . . . . . . . References II I Close 3 3 4 8 Quit Page 2 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au 1. Introduction The serious question of certainty in science was high-lighted by Heisenberg, in 1927, via his uncertainty principle [1]. He demonstrated the impossibility of specifying simultaneously the position and the speed (or the momentum) of an electron within an atom. In 1933, according to Wiener [7] a pair of transforms cannot both be very small. This uncertainty principle was stated in 1925 by Wiener, according to Wiener’s autobiography [8, p. 105-107], at a lecture in Göttingen. The following result of the Heisenberg-Weyl Inequality is credited to Pauli according to Weyl [6, p. 77, p. 393-394]. In 1928, according to 2 Pauli [6] the less the uncertainty in |f |2 , the greater the uncertainty in fˆ , and conversely. This result does not actually appear in Heisenberg’s seminal paper [1] (in 1927). The following second order moment Heisenberg-Weyl inequality provides a precise quantitative formulation of the above-mentioned uncertainty principle according to W. Pauli. 1.1. Second Order Moment Heisenberg-Weyl Inequality ([3, 4, 5]): 2 For any f ∈ L (R), f : R → C, such that Z 2 kf k2 = |f (x)|2 dx = E|f |2 , R On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 3 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au any fixed but arbitrary constants xm , ξm ∈ R, and for the second order moments Z 2 (µ2 )|f |2 = σ|f |2 = (x − xm )2 |f (x)|2 dx, ZR 2 2ˆ 2 (ξ − ξm ) f (ξ) dξ, (µ2 ) fˆ 2 = σ ˆ 2 = | | f | | R the second order moment Heisenberg-Weyl inequality 2 σ|f |2 (H1 ) · σ2ˆ 2 |f | On The Sharpened Heisenberg-Weyl Inequality kf k42 ≥ , 16π 2 John Michael Rassias holds. Equality holds in (H1 ) if and only if the generalized Gaussians f (x) = c0 exp (2πixξm ) exp −c (x − xm )2 Contents hold for some constants c0 ∈ C and c > 0. 1.2. Fourth Order Moment Heisenberg-Weyl Inequality ([3, pp. 26-27]): kf k22 2 R JJ J II I Go Back 2 For any f ∈ L (R), f : R → C, such that = R |f (x)| dx = E|f |2 , any fixed but arbitrary constants xm , ξm ∈ R, and for the fourth order moments Z (µ4 )|f |2 = (x − xm )4 |f (x)|2 dx and ZR 2 (µ4 ) fˆ 2 = (ξ − ξm )4 fˆ(ξ) dξ, | | R Title Page Close Quit Page 4 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au the fourth order moment Heisenberg-Weyl inequality 1 2 E2,f , (µ4 )|f |2 · (µ4 ) fˆ 2 ≥ 4 | | 64π (H2 ) holds, where Z h i 2 2 2 (1−4π 2 ξm xδ ) |f (x)|2 − x2δ |f 0 (x)| − 4πξm x2δ Im(f (x)f 0 (x)) dx, E2,f = 2 R with xδ = x − xm , ξδ = ξ − ξm , Im (·) is the imaginary part of (·), and |E2,f | < ∞. The “inequality” (H2 ) holds, unless f (x) = 0. We note that if the ordinary differential equation of second order (ODE) John Michael Rassias Title Page fα00 (x) = −2c2 x2δ fα (x) αx On The Sharpened Heisenberg-Weyl Inequality Contents 1 2 k 2 2 holds, with α = −2πξm i, fα (x) = e f (x), and a constant c2 = > 0, k2 ∈ R and k2 6= 0,then “equality” in (H2 ) seems to occur. However, the solution of this differential equation (ODE), given by the function p 1 1 2 2 2πixξm |k2 | xδ + c21 J1/4 |k2 | xδ , f (x) = |xδ |e c20 J−1/4 2 2 in terms of the Bessel functions J±1/4 of the first kind of orders ±1/4, leads to a contradiction, because this f ∈ / L2 (R). Furthermore, a limiting argument is required for this problem. For the proof of this inequality see [3]. It is open to investigate cases, where the integrand on the right-hand side of integral of E2,f will be nonnegative. For instance, for xm = ξm = 0, this JJ J II I Go Back Close Quit Page 5 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au integrand is: = |f (x)|2 − x2 |f 0 (x)|2 (≥ 0). In 2004, we ([3, 4]) generalized the Heisenberg-Weyl inequality and in 2005 we [5] investigated a Heisenberg-Weyl type inequality without Fourier transforms. In this paper, a sharpened form of this generalized Heisenberg-Weyl inequality is established in Fourier analysis. We state our following two pertinent propositions. For their proofs see [3]. Proposition 1.1 (Generalized differential identity, [3]). If f : R → C is a k complex valued function of a real variable x, 0 ≤ 2 is the greatest integer dj ≤ k2 , f (j) = dx j f , and (·) is the conjugate of (·), then (*) f (x) f (k) (x) + f (k) (x) f¯ (x) = [ k2 ] X i=0 On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias k (−1) k−i i k−i i 2 dk−2i (i) , f (x) dxk−2i holds for any fixed but arbitrary k ∈ N = {1, 2, . . .}, such that 0 ≤ i ≤ i ∈ N0 = {0, 1, 2, . . .}. Title Page Contents k 2 for Proposition 1.2 (Lagrange type differential identity, [3]). If f : R → C is a complex valued function of a real variable x, and fa = eax f , where a = −βi, √ with i = −1 and β = 2πξm for any fixed but arbitrary real constant ξm , as well as if p 2 Apk = β 2(p−k) , 0 ≤ k ≤ p, k and p p Bpkj = spk β 2p−j−k , 0 ≤ k < j ≤ p, k j JJ J II I Go Back Close Quit Page 6 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au where spk = (−1)p−k (0 ≤ k ≤ p), then (LD) p X 2 (p) 2 X fa = Apk f (k) + 2 Bpkj Re rpkj f (k) f (j) , k=0 0≤khj≤p holds for any fixed but arbitrary p ∈ N0 , where (·) is the conjugate of (·), and k+j rpkj = (−1)p− 2 (0 ≤ k < j ≤ p), and Re (·) is the real part of (·). On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 7 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au 2. Sharpened Heisenberg-Weyl Inequality We assume that f : R → C is a complex valued function of a real variable x (or absolutely continuous in [−a, a], a > 0), and w : R → R a real valued weight function of x, as well as xm , ξm any fixed√but arbitrary real constants. Denote fa = eax f , where a = −2πξm i with i = −1, and fˆ the Fourier transform of f , such that Z Z −2iπξx fˆ (ξ) = e f (x) dx and f (x) = e2iπξx fˆ(ξ) dξ. R R Also we denote On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Z w2 (x) (x − xm )2p |f (x)|2 dx, ZR 2 (µ2p ) fˆ 2 = (ξ − ξm )2p fˆ(ξ) dξ | | R (µ2p )w,|f |2 = 2 the 2pth weighted moment of 2 x for |f | with weight function w : R → R and the 2pth moment of ξ for fˆ , respectively. In addition, we denote hpi p−q p p Cq = (−1) , if 0 ≤ q ≤ = the greatest integer ≤ , p−q q 2 2 Z hpi 2 Iql = (−1)p−2q wp(p−2q) (x) f (l) (x) dx, if 0 ≤ l ≤ q ≤ , 2 R Title Page Contents JJ J II I Go Back Close q Quit Page 8 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au p−2q Z wp(p−2q) Iqkj = (−1) (x) Re rqkj f (k) (x) f (j) (x) dx, R if 0≤k<j≤q≤ hpi 2 , k+j where rqkj = (−1)q− 2 ∈ {±1, ±i} and wp = (x − xm )p w. We assume that all these integrals exist. Finally we denote Dq = q X l=0 Aql = β l 2(q−l) , Bqkj = sqk with β = 2πξm , and sqk = (−1) , and Ep,f holds for p ∈ N. In addition, we assume the two conditions: q q β 2q−j−k , k j P = [p/2] q=0 Cq Dq , if |Ep,f | < ∞ r (−1) lim |x|→∞ r=0 wp(r) 2 (p−2q−r−1) (l) (x) f (x) = 0, r=0 JJ J II I Close Page 9 of 18 p−2q−1 (2.2) Contents Quit for 0 ≤ l ≤ q ≤ p2 , and X Title Page Go Back p−2q−1 (2.1) On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias p , where 2 q−k X Bqkj Iqkj , 0≤khj≤q if |Dq | < ∞ holds for 0 ≤ q ≤ q 2 X Aql Iql + 2 r (−1) lim |x|→∞ wp(r) (x) Re rqkj f (k) (x) f (j) (p−2q−r−1) (x) = 0, J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au for 0 ≤ k < j ≤ q ≤ p . Also, 2 q ∗ 2 |Ep,f | = Ep,f + 4A2 (≥ |Ep,f |), where A =R kuk x0 − kvk y0 , with L2 −norm k·k2 = (|u| , |v|) = R |u| |v|, and R R |·|2 , inner product u = w(x)xpδ fα (x), v = fα(p) (x); Z Z x0 = |ν(x)| |h(x)| dx, y0 = |u(x)| |h(x)| dx, R R On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias as well as 2 1 − 1 x−µ h(x) = √ √ e 4( σ ) , 4 2π σ where µ is the mean and σ the standard deviation, or s Γ n+1 1 1 2 h(x) = √ · , n+1 4 nπ Γ n2 x2 4 1+ n where n ∈ N, and 2 Contents JJ J II I Go Back Z kh(x)k = Title Page 2 |h(x)| dx = 1. Close R Theorem 2.1. If f ∈ L2 (R) (or absolutely continuous in [−a, a], a > 0), then q q 1 q p ∗ ∗ 2p √ (Hp ) (µ2p )w,|f |2 2p (µ2p ) fˆ 2 ≥ E p,f , | | 2π p 2 holds for any fixed but arbitrary p ∈ N. Quit Page 10 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au Equality holds in (Hp∗ ) iff v(x) = −2cp u(x) holds for constants cp > 0, and any fixed but arbitrary p ∈ N; cp = kp2 /2 > 0, kp ∈ R and kp 6= 0, p ∈ N, and A = 0, or h(x) = c1p u(x) + c2p v(x) and x0 = 0, or y0 = 0,where cip (i = 1, 2) are constants and A2 > 0. Proof. In fact, from the generalized Plancherel-Parseval-Rayleigh identity [3, (GPP)], and the fact that |eax | = 1 as a = −2πξm i, one gets (2.3) Mp∗ On The Sharpened Heisenberg-Weyl Inequality 1 = Mp − A2 2p (2π) John Michael Rassias 1 · (µ2p ) fˆ 2 − A2 | | (2π)2p = (µ2p )w,|f |2 Z 2p 2 2 = w (x) (x − xm ) |f (x)| dx R Z 2 1 2p ˆ · (ξ − ξm ) f (ξ) dξ − A2 2p (2π) R Z 1 = w2 (x) (x − xm )2p |fa (x)|2 dx 2p (2π) R Z (p) 2 2 · fa (x) dx − A R (2.4) = 1 kuk2 kvk2 − A2 2p (2π) Title Page Contents JJ J II I Go Back Close Quit Page 11 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 (p) with u = w(x)xpδ fα (x), v = fα (x). http://jipam.vu.edu.au From (2.3) – (2.4), the Cauchy-Schwarz inequality (|u| , |v|) ≤ kuk kvk and the non-negativeness of the following Gram determinant [2] kuk2 (|u| , |v|) y0 (2.5) 0 ≤ (|v| , |u|) kvk2 x0 y0 x0 1 = kuk2 kvk2 − (|u| , |v|)2 − kuk2 x20 − 2(|u| , |v|)x0 y0 + kvk2 y02 , 0 ≤ kuk2 kvk2 − (|u| , |v|)2 − A2 On The Sharpened Heisenberg-Weyl Inequality with John Michael Rassias Z A = kuk x0 − kvk y0 , x0 = Z |ν(x)| |h(x)| dx, y0 = R and 2 |u(x)| |h(x)| dx, R Z kh(x)k = Contents 2 |h(x)| dx = 1, R we find (2.6) 1 (|u| , |v|)2 (2π)2p Z 2 1 = |u| |v| (2π)2p R Z 2 1 (p) wp (x) fa (x) fa (x) dx , = (2π)2p R Mp∗ ≥ Title Page JJ J II I Go Back Close Quit Page 12 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au where wp = (x − xm )p w, and fa = eax f . In general, if khk = 6 0, then one gets (u, v)2 ≤ kuk2 kvk2 − R2 , where R = A/ khk = kuk x − kvk y, such that x = x0 / khk , y = y0 / khk. In this case, A has to be replaced by R in all the pertinent relations of this paper. From (2.6) and the complex inequality, |ab| ≥ 12 ab + ab with a = (p) wp (x) fa (x), b = fa (x), we get Z 2 1 1 (p) ∗ (p) (2.7) Mp = wp (x) fα (x)fα (x) + fα (x)fα (x) dx . (2π)2p 2 R From (2.7) and the generalized differential identity (*), one finds 2 Z [p/2] p−2q X 2 1 d (2.8) Mp∗ ≥ 2(p+1) 2p wp (x) Cq p−2q fa(q) (x) dx . 2 π dx q=0 R From (2.8) and the Lagrange type differential identity (LD), we find Z [p/2] q p−2q X X 2 1 d ∗ Mp ≥ 2(p+1) 2p wp (x) Cq p−2q Aql f (l) (x) 2 π dx R q=0 l=0 2 X +2 Bqkj Re rqkj f (k) (x) f (j) (x) dx . 0≤khj≤q On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 13 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au From the generalized integral identity [3], the two conditions (2.1) – (2.2), and that all the integrals exist, one gets Z Z 2 2 dp−2q (l) p−2q wp (x) p−2q f (x) dx = (−1) wp(p−2q) (x) f (l) (x) dx = Iql , dx R R as well as Z dp−2q wp (x) p−2q Re rqkj f (k) (x) f (j) (x) dx R Z p−2q (p−2q) (k) (j) = (−1) wp (x)Re rqkj f (x) f (x) = Iqkj . On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias R Thus we find Title Page Mp∗ ≥ = 1 22(p+1) π 2p 1 22(p+1) π 2p [p/2] X Cq q=0 q X l=0 2 Aql Iql + 2 X Bqkj Iqkj 0≤khj≤q 2 Ep,f , P[p/2] where Ep,f = q=0 Cq Dq , if |Ep,f | < ∞ holds, or the sharpened moment uncertainty formula q p 1 q 1 p p 2p ∗ √ √ Ep,f ≥ |Ep,f | , Mp ≥ 2π p 2 2π p 2 Contents JJ J II I Go Back Close Quit Page 14 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 where Mp = Mp∗ + 1 A2 . (2π)2p http://jipam.vu.edu.au We note that the corresponding Gram matrix to the above Gram determinant is positive definite if and only if the above Gram determinant is positive if and only if u, v, h are linearly independent. Besides, the equality in (2.5) holds if and only if h is a linear combination of linearly independent u and v and u = 0 or v = 0, completing the proof of the above theorem. Let Z (m2p )|f |2 = x2p |f (x)|2 dx R th 2 be the 2p moment of x for |f | about the origin xm = 0, and Z 2 2p ˆ (m2p ) fˆ 2 = ξ f (ξ) dξ | | R 2 the 2pth moment of ξ for fˆ about the origin ξm = 0. Denote p p! p−q p−q εp,q = (−1) · , p − q (2q)! q if p ∈ N and 0 ≤ q ≤ p2 . Corollary 2.2. Assume that f : R → C is a complex valued function of a real variable x, w = 1, xm = ξm = 0, and fˆ is the Fourier transform of f , described in our theorem. If f : R → C (or absolutely continuous in [−a, a], a > 0), then the following inequality v 2 u [p/2] u q q X u 1 p 2p t √ (Sp ) (m2p )|f |2 2p (m2p ) fˆ 2 ≥ εp,q (m2q ) f (q) 2 + 4A2 , p | | | | 2π 2 q=0 On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 15 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au holds for any fixed but arbitrary p ∈ N and 0 ≤ q ≤ p2 , where Z 2 (m2q ) f (q) 2 = x2q f (q) (x) dx | | R and A is analogous to the one in the above theorem. We consider the extremum principle (via (9.33) on p. 51 of [3]): 1 , p∈N 2π for the corresponding “inequality” (Hp ) [3, p. 22], p ∈ N. Problem 1. Employing our Theorem 8.1 on p. 20 of [3], the Gaussian function, the Euler gamma function Γ, and other related special functions, we established and explicitly proved the above extremum principle (R), where Γ p + 12 , R(p) = P [p/2] p p! p−q Γq q=0 (−1) p−q · (2q)! p−q q R(p) ≥ (R) with [q/2] X q 2 1 1 2 2 Γ k+ Γq = Γ 2q − 2k + 2k 2 2 k=0 q q X k+j k+j +2 (−1) 2 2k 2j 0≤k≤j≤[q/2] 1 1 1 ×Γ k+ Γ j+ Γ 2q − k − j + , 2 2 2 On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back 2k Close Quit Page 16 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au p! 0 ≤ 2q is the greatest integer ≤ 2q for q ∈ N ∪ {0} = N0 , pq = q!(p−q)! for p ∈ N, q ∈ N0 and 0 ≤ q ≤ p, p! = 1 · 2 · 3 · · · · · (p − 1) · p and 0! = 1, as well as √ 1 1 1 (2p)! √ Γ p+ = 2p · π, p ∈ N and Γ = π. 2 2 p! 2 Furthermore, by employing computer techniques, this principle was verified for p = 1, 2, 3, . . ., 32, 33, as well. It now remains open to give a second explicit proof of verification for the extremum principle (R) using only special functions techniques and without applying our Heisenberg-Pauli-Weyl inequality [3]. On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 17 of 18 J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au References [1] W. HEISENBERG, Über den anschaulichen Inhalt der quantentheoretischen Kinematic und Mechanik, Zeit. Physik 43, 172 (1927); The Physical Principles of the Quantum Theory (Dover, New York, 1949; The Univ. Chicago Press, 1930). [2] G. MINGZHE, On the Heisenberg’s inequality, J. Math. Anal. Appl., 234 (1999), 727–734. [3] J.M. RASSIAS, On the Heisenberg-Pauli-Weyl inequality, J. Inequ. Pure & Appl. Math., 5 (2004), Art. 4. [ONLINE: http://jipam.vu.edu. au/article.php?sid=356]. [4] J.M. RASSIAS, On the Heisenberg-Weyl inequality, J. Inequ. Pure & Appl. Math., 6 (2005), Art. 11. [ONLINE: http://jipam.vu.edu. au/article.php?sid=480]. [5] J.M. RASSIAS, On the refined Heisenberg-Weyl type inequality, J. Inequ. Pure & Appl. Math., 6 (2005), Art. 45. [ONLINE: http://jipam.vu. edu.au/article.php?sid=514]. [6] H. WEYL, Gruppentheorie und Quantenmechanik (S. Hirzel, Leipzig, 1928; and Dover edition, New York, 1950). [7] N. WIENER, The Fourier Integral and Certain of its Applications (Cambridge, 1933). On The Sharpened Heisenberg-Weyl Inequality John Michael Rassias Title Page Contents JJ J II I Go Back Close Quit Page 18 of 18 [8] N. WIENER, I am a Mathematician (MIT Press, Cambridge, 1956). J. Ineq. Pure and Appl. Math. 7(3) Art. 80, 2006 http://jipam.vu.edu.au